I'm sure you would expect anyone who contacts you to send their funds first. Then leave you with the discretion of deciding to pay them or not. How would the person be sure you'll not just decide if the "windfall" isn't tempting enough to walk away with? In other words, you could decide to steal their money and there's nothing they could do about it. If you're serious about your exchange business, join an established exchange that has built-in security measure in their P2P section. No one would take you serious here unless they want to risk losing their funds.