>My contract actually states that copyrights are transferred when final payment is received.

Indeed.

I had one guy who was absolutely insisting he would pay me the balance the day *after* I sent him the source code.
I said, read the contract - I get paid *before* you get the source.

He yelled and threatened legal action - over the difference of which went first, source delivery or payment.

I called his bluff - if you don't have $3,200 to pay me, you can't afford a lawyer.

It took him another 2 months to actually pay the money.

There is no doubt that I would never have seen the final payment were it not for the contract.