Can i Get sued for selling an iphone with a bad esn?

So i posted an iphone 5 for sale on Craigslist. I buy to resale, so i bought an iphone 5 of a guy he told me it had a Clean esn, but durning the transaction i put HIS sim card in the work to check if it worked. It worked great but his number is programed in the phone but i didn't think much about it. So i posted the the phone for sale and the ad said it was perfect and clean esn. So i sold it to someone on CL. And now i'm getting calls from them saying they are gonna sue me for fraud because i sold them a phone with a Bad esn. They went to take it to sprint to activate it. And they told them that the device was still under the account of the sim. Please note that the phone is NOT reported stolen. They told me they were gonna sue me and that they have an a uncle that is a detective. So i feel like i did nothing wrong and i wanna know if i can get sued for this?

No, but its most likely because you bailed out of your contract. That's something you should have listed, and yes it is fraud if its not transferrable as you listed.

Yea, you might want to figure out how iphones work a little better. You did actually screw up the phone by putting the guy's sim card in. Had you not done this, Sprint might have been able to fix it, they probably can't now. Nor can an apple store. He should have contacted / gone to a Sprint store immediately, and you shouldn't have messed with it.