I just sold my car and want to wire the money back to the states.

If the bank asks for proof of purchase, what do I show them?

I do have a a bill of sale that I made for myself and the buyer but is that proof enough since the bank has no way to determine if the price is real?

Well, if the bank wants something showing you originally "brought money into the kingdom" to originally buy the car, a bill of sale won't hack it because that's just money exchanging hands "within Thailand"...money exchanges hands everyday in Thailand millions of times every day. I recommend you just go to the bank to attempt the transfer and if they don't do the transfer they can tell you what document(s) is needed but take along any documents you think might help, to include documents showing where you have transferred money "into Thailand" like maybe you did when originally buying the car.

Edited July 29, 201411 yr by Pib

If all else fails, take cash out if its an option.