If at all there is any benefit. What is the point of selling off the private key if you can also benefit the private key and the adddress/
Since mentioned something about ICO, maybe OP participated in the ICO (invested some money) and the buyer can get rewards from ICO contribution.
OP can still access the wallet right after selling the private keys but if they are not the scammer, they should let the buyer transfer the funds first into another wallet. That should do the job but there will be no mention about that hence not a guaranteed one.
What only got me thinking is why would tezos and cosmos do an ICO this year because I think these two projects are not new anymore. What if these were the fake projects because we have lots of them right now that their names are identical to the original/reputed projects.