I don't care to know the reason why he would want to buy your gambling account, but if you have already done a kyc verification in that account, do not sell. The buyer will likely comes up with the excuse of location restrictions or needing a high rank account without having to gamble too much, but don't fall for such excuses if you have already done a kyc, because it's just to risky.
I believe even if the KYC was not required, there are still problems in selling an account. While you might believe that you have given everything away, if the buyer goes on to use the account for something that violates the platforms policies, your information may still be associated with the account. Some individuals might be only focused on the money they might make from the deal and they don't bother to think about the potential problems that might come after that. Well it's not worth the risk at all.