I brought an iPhone sold it now the buyers saying its barred?

About 6 months ago I brought an iPhone off a decent looking bloke at the time, a week after I dropped it smashed the screen so I got a new one and threw that to the back of my drawer, last week I remembered it tried to turn it on but no response atall, I tried everything but alas I had to sell it to someone with more knowledge, he brought it off me and a week later started ringing me threatening me saying its blocked. My thoughts where he had tampered with it at first but then I thought maybe the bloke I brought It off had intended to defraud me, so my question is if I had no way to know the phone was barred/blocked how is this my fault? As far as I'm concerned he's lucky he got it on

Added (1). Clearly people don't get the idea, my second phone wasn't an insurance job, i went out and brought a new phone, i didn't have insurance

About 6 months ago I brought an iPhone off a decent looking bloke at the time, a week after I dropped it smashed the screen so I got a new one and threw that to the back of my drawer,
--- ok, you got an iphone… It broke… You did an insurance replacement… Makign the carrier block the ESN of the first phone (BAD ESN--non flashable to any account on Earth)… Got the new iphone… And partied on… Ok… Next…

last week I remembered it tried to turn it on but no response atall, I tried everything but alas I had to sell it to someone with more knowledge, he brought it off me and a week later started ringing me threatening me saying its blocked.
--- well… Yeah… Duh… You got an insurance repalcement… The carrier blocked the ESN, per insurance policy… Lmao! Do people read the wireless insruance brochures!

My thoughts where he had tampered with it
---no… Only the carrier has access to your ESN… And its ALWAYS the carrier that blocks the ESN

at first but then I thought maybe the bloke I brought It off had intended to defraud me,
--- if this was the case, you would have lost service on the first iphone within hours/days of buying it! ANd when you broke it, you would NOT be allowed an insurance repalcement.

so my question is if I had no way to know the phone was barred/blocked how is this my fault?
--- it is your responcibility as the owner to know the policies and procedures of your wireless carrier and insurance program… Per law.

As far as I'm concerned he's lucky he got it on
--- as for as he's concerned, you just scammed him… Big time… Which is fraud, regardless of you knew about the BAD ESN or didn't know about the BAD ESN… Federal Law does nto discriminate against this… And since no contract was signed at the time of purchase (you take this deviec "as is" and i'm under no legal responicibility to accept returns or give refunds", i highly suggest you repay him… If he was smart, he can sue you to high heaven… I would… Lol