It is the rate at which you buy, you give 20 usd and receive 19.71 usdt. I see that the rate is 1.012

Hello, I have a question. I am new, because when I buy in p2p for example 20usd, I get 19.71usdt. Is it not supposed that there are no commissions and that 1usd=1usdt? Where do those 30 cents go?