What’s so hard to understand? We’ve established that before about 3:30 P.M. on 3/27/14, dolphinboy, not to mention me, and probably a lot of other people, thought that when the issuing bank cleared the money to be transferred to your bank and thence into your account, that meant that the check had been declared valid, and there were no backsies.
We know different now, but it’s not an assumption made only by dumb people, thank you very much. 
The US banking system needs to jump on the Interac money transfer system.
I can send up to $2000 to any person I want and the only information I need is their email address.
My bank generates a code based on information I provide them and sends an email to my recipient. They click on the link in the email, enter the password which I have provided them directly (in business situations this is often an invoice number), and then log into their own online banking and the money is deposited.
Actually I lied, I don’t even need an email address anymore. There is now an option to text the link to their cell phone instead.
It’s completely free, as secure as the users let it be (don’t text a transfer to someone and text them the password, same with email. Use different methods JIC of a lost device), and if for some reason the person doesn’t claim the money it goes back into my account after 14 or 30 days. I can’t remember which since no one ever turns down my cash 
Ever pay a bill online?
If you used a checking account, you did exactly what the check sorters do - T/R, account, amount, date of the “From” account. The software provides the “To” side.
The only credible reason I can come up with (aside from history) is that a “wire transfer” needs the header and trailer (the Fed uses batch controls to ensure balance) records for each transaction, and the Fed may charge by “batch”.
With online payments, that charge is either no longer there or the software is collecting enough individual payments to distribute the batch charge among 1000’s of transactions.
That CACHA system I mentioned - California Account Clearing House Association - this was Uncle Ronnie’s “Private Enterprise can do everything better and cheaper than the Government” bit. A group of CA banks decided they could set up their own Clearing House and process checks more cheaply than the Fed.
They used the Fed’s format and algorithms. Just so you know: the Fed transactions were formatted on 80 byte records. Yep: card image, for those who know the term.
Others" the IBM 5081 card “IBM Card” was a chipboard card with 80 positions keyed by punched holes using the Hollerith code, first devised in 1880 for the US Census.
Those cards will outlive all of us.
No, I meant, why would anyone write a check (or money order or whatever) for well over the amount of the transaction and ask for the excess to be sent back to him or to somewhere else – unless it was a scam? And accordingly, why would the person receiving such a check or money order ever agree to do so?
Is there any common or legitimate reason for a transaction to be done that way?
If a seller tries to sell a widget on e-Bay, and a buyer suggests that he will send $200 over the asking price, with instructions about what I should do with that excess $200, why in the world would any seller NOT be all :dubious: ?
…because its easy money and they don’t know about or even contemplate that it could be a scam. The scams have just enough plausibility that some people believe what they are told. Its simple human nature. They don’t need a lot of people to fall for the con: just a few.
One possibility:
I buy a widget from you for $100. You tell me you’ll send the widget as soon as you receive payment. I send you a check for $300. You tell me of the error. I say, “Aw, heck. Sorry about that. My bad. Listen, I don’t want to write another check, and you don’t want to wait for another check to arrive. Just deposit the oversized check and, after it clears, wire me the excess $200. I trust you.”
I have and it’s been around a long time. NY Times, 7 years ago:
The NY Daily News, more recently:
And tips on recognizing forged USPS money ordershttp://flakelist.org/forum/viewtopic/topic/204:
I suppose the post office would indeed be able to tell the difference between a genuine one and a fraud. But most people won’t bring the money order to the post office; they’ll deposit it in their bank account, and therein lies the whole problem of confusing "it cleared’ with “I have nothing to worry about”.