Sorry for your loss!
But, it sounds like you got conned.
1. You loaned a guy your balanced R10 for possible trade.
2. They came back single ended, in a condition that you didn't loan them out in or request that he change them to.
3. They arrived back on your doorstep unannounced 3 months later.
I'd bet mad as fuck, but you are taking this like it's nothing. I'd be at the mans doorstep, bat in hand ready to commits that ass whopping! Just saying