Borrower accepted and confirmed $100, with a promise to repay $150 the following day. Rather than pay the amount interest as promised, borrower merely issued (on the due date) a Paypal refund for the principal amount alone.

He pretended to be surprised at the refund, and asked me why I did it. Not that I needed to, but just to be sure I wasn't completely insane, I called Paypal and asked what happened. Paypal confirmed to me that he had issued the refund and further confirmed that, in any case, only a recipient can issue a refund.

Since I'm new around here, I asked if an unpaid post is appropriate given that I did indeed get my principal back. /u/FoxK56 said that this is the correct thing to do, so here it is.

Happy to answer any questions about my experience with this borrower.

[EDIT: I also have a screen shot showing that he used the money to pay a bill to someone else immediately after he received the transfer from me. He was clearly in this for a free float.]