I hear occasional mad laughter.
I think it’s coming from me.
“Hey, i collect coins, that could help my collection, mind if I exchange it for double the coin?”
If I was the clerk, that would have my bullshit detector buzzing up a storm. Just tell them what it’s worth and feel like you did someone (who could probably use the money more than you) a solid.
Why wouldn’t you pay what the coin is worth?
You do notice, because that’s the hypothetical. 
If it helps, pretend that before visiting the cafe, you were stuck in a waiting room for hours with no entertainment other than a documentary on this exact coin looping on the TV. Even with no prior numismatic interest, you have coincidentally become an expert at distinguishing this one particular coin.
Then it’s easy. I say, hey, that’s incredibly weird! I just watched a video about this exact coin. It’s worth a lot of money. You should try to sell it to a collector.
What is a rare coin worth? See, there’s a huge gap between what you can sell it for, compared to what you would buy it for. Then, the all important thing- Condition, How do you tell the condition without closely examining it, and checking vs expert sources?
And look- I spotted the coin, otherwise it would go into a coin machine at the bank or something. Let us say the coin is worth say- $10- i.e. that is how much I’d buy it for- graded and in a slip. But it is not graded and not in a slip. If the clerk took it to a coin store, they’d be offered a few bucks- then there’s that drive to the store, their time etc. So, say it is a quarter, I am offering 50cents. For me, it fills a hole in a collection. For them? Net (after time, gas, etc) that is about what it is worth.
Because the poll question specifically says you can?
And the poll question says you know it’s worth about $100. That’s worth some time and gas.
Sure, but does the clerk know that? And how on earth do you know that- i doubt if the coin is in a graded slip. And how much would the coin shop offer them? $30?
At a garage sale, do you tell the seller what things are worth? I mean, i watch Antiques Roadshow. You make an offer- if that is accepted- then it is a Fair market value transaction. You have told the clerk it is collectable, the clerk now knows it is now worth more than 25 cents. They can counter offer, or look it up on the internet- if they choose not to look it up- how is that your fault? I mean, everyone carries a cell phone now. Maybe they dont want to both with all that.
And assume it is worth $100 at a shop- not to me- ungraded. Sure, after the shop has done their work- spending their expert time- and then they grade it.
Isnt expert time worth something?
No. It takes about 2 seconds for you to tell the clerk what it is worth and congratulate them on their good fortune. I enjoy a good bargain as much as the next guy but not by exploiting the seller’s ignorance (especially one who’s income comes partially from tips).
Again, the coin isnt in a graded slip. And what is the worth? What I would have to pay for it in a coin shop (and obviously, it isnt worth that to me, otherwise I would have already done it) or how much the coin shop would pay you? Look up Fair Market Value someday.
You tell them it is collectable, and make an offer. Then, they can say NO, or look it up, or accept your offer. That is how Fair Market value works. By informing them of possible value (it is collectable), the ball is in their court. You arent stealing, they can say NO. If they dont want to look it up, how is that on me?
Note, i did not exploit any ignorance- I said it was collectable. I gave that info for free.
You know almost exactly what it is worth. Go back and read the poll question!
Yes, again-
is the “worth” retail or wholesale? The poll did not make that clear.
You’re spending a lot of verbiage to justify not doing what I would consider just doing the right thing. You do you.
Why doesnt the clerk look it up after you have informed them? Am i holding a gun to their head? Cant they just say “No thanks”?
And say i do tell the clerk that- can the clerk then take it out of the jar for themselves without telling the owner? Will the owner want a share- or just the whole coin (less face value)?
At least that’s an improvement over your original plan to rip the guy off. There’s hope yet.
The tips are supposed to go to the workers, not to the owner.
Supposed to. But if the owner takes the valuable quarter and replaces it, then the clerk is Shit out of Luck. And the clerk cant just help himself, those tips must be shared. So, even if I tell the clerk, that coin might be worth maybe $100, what’s gonna happen?
There’s no way I’d fish it out & offer fave value as that makes it an impulse purchase with the onus on me to do work to get my money back for something I didn’t want & dont want to keep