Sold iPhone on ebay now buyer wants me to unlock it?

I recently sold my old iPhone 4s on ebay. The buyer contacted me a few days ago asking if I could go to att.com/deviceunlock and unlock it. It's free to me and he said he would gift me $20 on paypal if I do it. Is this legit or is this guy trying to pull something on me? It has a clean imei so it wouldn't be an issue, I just don't know if this is something that is going to get me into trouble

No there's no trouble. He must have another carrier so he can't use the phone while it is locked to ATT.

ITS OK. He just wants to use it on another carrier like tmobile.

i also did it but with a iphone 4 on att and got it unlocked from the buyer so that i could use it on tmobile.

unlocking it won't mess with the IMEI at all, it only lets him use the phone on other carriers like tmobile, sprint, us cellular and other world wide carriers since its GSM

Yes unlock his phone for 20 do it from a different website not the one he recommends it will get unlocked either way but do it from a free and secure website easy $20 yes it's legit aswell go for it

If he has the phone, my advice is don't get involved.