quick serious question
when you say "friend", is this a recent new-ish friend, as in, I've known him for just a few years now & done some business and had a coffee at his place on a Saturday & kicked some tyres?
To me, friends are people you know well, both socially & in business & who would NOT stitch you up.
I know a guy I would consider a friend, he's a builder, but I call him a friend as I've got to know him over 4 years doing things on my house bl4hbl4h, we helped him try to save his local school from closure by writing some supporting letters, I have his mobile number (a weird but valid modern sign of friendship), we exchange xmas cards bl4hbl4h, but if I found out he had bodged work on my house, then I would say "all bets are off", the friendship wouldn't help, he's for the high jump.
You really have to take a step back here and ask that big question of yourself; if you knew it was a dodgy bike, would you sell it on to a mate? I bet not.
I don't actually "know" anyone really on this forum in the face to face pop to the pub sense (I've met just 4 of the members), but I wouldn't do that to anyone on here by example, I wouldn't do it to anyone, and the internet is pretty much anonymous. So this guy who sold you this bike falls into the "not worth having as a mate" category, sorry that may seem harsh, but that's how I see it.
Lastly, as John said, a bent frame, Cat D? errrmmm, sounds iffy to me. Isn't Cat D the lower end entry level damage category? ie: in some cases broken plastics and a few scuffs?