I’d return it.
I still remember the time a clerk accidentally charged me only the normal size price for a king size junior mints and I didn’t say anything.
This is why everybody should be required to work in retail for a year.
I handle money in the job I have now. If I come up $40 short at the end of the day, I won’t get fired. But I will get written up. This will negatively affect my yearly performance review. Which means I will get less of a raise or no raise at all.
So you might think you’ve snagged $40 from a big faceless corporation, but really you’ve taken money directly out of my pocket. And not just $40, either. Because of your selfishness, I’ll be spending another year earning $6.75 an hour instead of the $7.00 an hour I’d be making if I hadn’t been written up. That’s $312 you stole from me.
Enjoy your windfall, asshole.
With that final admonition not being directed at any specific person in this thread, as this is not The Pit and nobody is perfect.
Let’s get off the firing aspect, OK? It is very likely that here in the US an employee would be responsible for the shortage. Keeping the $40 is like taking it out of his pocket. It seems a high price to pay for a simple mistake. And to respond to a previous post of yours, “finders keepers” is a rather juvenile justification, don’t you think? Do adults really say that?
If, after I get home, I discover that I have an extra buck in my change, I probably wouldn’t bother to do anything about it.
An extra fifty is another story. If I am unable to return to the store right away, I would probably call them and arrange to return it the next day.
Okay, for the sake of argument, let’s say that the employee won’t lose his or her job. How do you know that he won’t be disciplined in some other manner?
The fact is, you don’t. You don’t know how severe the repercussions would be. Give the money back.
I’d curse a lot, then return the money. I’m not at all religious, and no paragon of morality either, but I do feel guilt when I do something “questionable”.
Just recently, I was shopping in a Sears store attached to a mall, and I picked up an item of clothing. Then I looked at fifty other things, left the store, and walked clear to the other end of the mall before realizing I was still carrying that item of clothing. I cursed a lot, then took a long, long walk back to the Sears cashier.
I must say I’m also surprised at the results of this poll. Other Dopers are usually a hell of a lot more likely to do the right thing than I am. 
Return it - it’s not yours.
The only time I’ve kept too much change was when I innocently said to the lady who was doing the cashing out “excuse me, you’ve given me the wrong change”. Her response: “I most certainly did not, I don’t make mistakes!” in her haughtiest voice.
So I put the money in my pocket and left. (If I remember correct, it was change for a $20 instead of a $10).
But then our money is all different colours, so it’s generally easy to spot a boo boo. 
I’d give it back. Even if no one would get in trouble were I to keep it; even if no one would know. *I’d * know.
Return it, absolutely.
One time at college, I had to stop another girl when she took her mittens out of her pocket and a dollar bill floated out. I picked it up, and the bad Snicks on my shoulder said, “You know, you could just keep that. It’s not much.” I ran up to her and tapped her shoulder and returned it. Even though it’s just a dollar, I knew there was times when I depended on having every penny to get lunch. If it had been me, I would’ve missed that dollar, so I gave it back.
Another time, SpouseO and I were eating out at a new place, and when our server brought the bill, she’d only charged us for the drinks; the sandwiches we’d enjoyed weren’t listed. We called her over and pointed out the error. She thanked us profusely, saying “A lot of people woudn’t have done that.” I’m guessing she would’ve had to make up the difference out of her own pocket, and I’m not about to do that to someone else.
It’s just the right think to do.
$40 is a lot. A dollar, maybe even 5, I’d keep walking with. $40?
I’ve also worked as a cashier, and the place I worked at happened to be unrelentingly strict. If your drawer didn’t match at the end of the day by one penny, you got written up. Second offense, have a “counseling” with the boss. Third offense, written, counseling, and you got put on probation.
Fourth offense? Fired.
Now I’ve been on both ends of the spectrum, as many of you have. $40 is too much to pocket and walk off. But neither do I feel any guilt in keeping that extra dollar or 5.
I’ve returned $10. Gave the cashier a $10, pocketed my change, at another store in the mall pulled out the change and realized the cashier gave me change for a $20. Went back to the original store and gave her the $10 back and was thanked profusely. I’d do the same for any amount.
If I didn’t realize it until I got home however, I don’t think I’d put the kids back in the car and drive 20 minutes to give the money back. In that case - where it would be pain for me to return the money, I’d probably just earmark it for charity.
I was just returning to this thread to post this suggestion.
The above situation has never happened to me because I count my change when I receive it. But if it did, I’d simply return to the store and say: “I think you gave me incorrect change.” If they are willing to correct the error without knowing who it will benefit, great. In most cases, I expect that I’d be told that their policy is that change is final when the customer has left the premises. Their loss.
Returning the money is unquestionably the only thing I’d do.
I got two $50s stuck together in change from taking my worldly wealth of a $100 bill and buying some ramen at Kroger’s, in a year where I was making very little, and was desperately poor.
I admit that I stared at that bill for several minutes before going back and returning it. That $50 would have filled my refrigerator and let me sleep easier for a couple of weeks. I was tempted, I admit.
But then I thought of every meal I’d eat, and how it would taste, knowing it was stolen…
I was told that in the U.K. the law is that as soon as you depart the checkout the bill stands.
That said, I’ve had to politely correct the person at the till more than once.
I’d bring it back, for all the right reasons.
And this isn’t just hypothetical, since I have been in situations where I received more from the clerk than I should have gotten. Though I don’t usually wait until I’m out the door before I notice the error…
I usually ask myself this question: “Self, if they had short-changed you this much, would you make them fix it?” If yes, I return the money, if no, I don’t. In other words, if I’m supposed to get 25 cents and I get 20 cents back instead and it’s super-busy, I’m probably not going to worry about my nickle. Or if I get all the way home and I find out my change is off by $2, I’m also not going to bother. Same with the other way.
I’m pretty sure that if I paid for something with a $100 bill, and I got home and the change was $40 short, I’d go try to get my money back. So in the reverse, I would definately return $40 extra dollars.
Final thoughts: I always count my change at the register, and I’ve also worked the register before. Coming up short sucks a lot, since the assumption is that you’re shorting the register for your own profit.
Actually, when i buy things with cash, i usually just stuff the change into my pocket along with the receipt. I very rarely count it.
Also, because i shove it into a pocket that probably also contains some other bills, it’s highly unlikely that i’d even notice whether i’d been the recipient of a stiffing or a windfall. And, to tell you the truth, it wouldn’t be the end of the world anyway, because i generally only use cash for small purchases anyway.
I like to think that if i were given too much change and i knew about it, that i would return it. I think it’s fucking outrageous that a clerk might be fired for an honest mistake like that, and i wouldn’t want to be the cause of their downfall.
At what amount do you draw the line? Someone certainly would be fired over a $100 or $500 mistake. When do you consider taking something that’s not yours stealing and when do you consider taking something that’s not yours a gift?
I always give it back. If you know it’s not yours and you keep it, it’s a form of stealing.
Lobsang said the same thing and when I asked for a cite admitted he had made it up. Actually, he said that once you were *out the door * the money was yours. Now it’s “once you depart the checkout.” Respectfully, this makes so little sense to me that I will have to ask for a cite. Any UK legal type Dopers want to chime in?