"Otherwise we cannot be not sure that we have really received the coins. "

You are operating an exchange, with a high skillset of technical skills. By seeing an exact inflow of coins, at the exact time, with all of my tx id's, amounts, specified time and even screenshots provided, that show that these coins were deposited to your exchange, it shouldnt take you more than few seconds to realise where they came from.

You are simply thinking that I (and other people reading this) must be a fool.