If it sounds too good to be true, then it probably is. Yes, you can be scammed.
Ask yourself why this user is willing to pay you 50% over the spot price? Even if AdvCash is the only payment method he can use, he could use it on a peer-to-peer exchange such as Bisq, LocalCryptos, or Hodl Hodl, and pay less than 1% over the spot price. Why would he pay 50% more for you?
Where did you come in to contact with this person? I'm going to guess it was on Telegram or some other site used predominantly by scammers which has no reputation system, and he wants to conduct the trade without using any escrow or trading platform. Tell him that you want to use a reputable escrow from this forum for the trade and when he comes up with some excuses about why he doesn't want to go ahead, you'll have your answer.
Thank you for answer!
He want to trade with paxfull. He did 14 trades on M-Pesa with KES currency (Kenya).
Also the question is - if he pay me, then I withdraw money from advcash and advcash do negative balance on my account. What is going to be next? If I use verified/unverified account advcash will try to catch me or scammer?