I guess there no experience cryptocurrency enthusiast here that wouldn't know the outcome or your intention,
Except if you at first allow the person get access to the wallet, which I believe you aren't going to do.
Best way or alternative for you is to find a centralized exchange and get registered then sell your crypto on the platform.
He's selling the private key and not crypto and no, there are experience crypto Enthusiasts here who are well aware of the dangers and scam surround buying private keys
He's not selling crypto but rather he want to sell a private key which have a link towards tezos and cosmos. And for sure he think his wallet have a value because his wallet has potential to get airdrops conducted by said chains. But I also guess no one will buy it knowing the risk since even if he sell it he can still access the wallet anytime he want.
Indeed, it's a waste of time and money even if the address has potential future airdrops. There is no guarantee that the person who sold the private key has a bot set up to sweep off any airdropped token that lands into the address is a matter of seconds.