Binance (and other exchanges) have buyers and sellers. If you buy 0.0001 BTC, you are buying from a seller. If you are buying from the exchange, then the exchange is acting as the middle man.
When you first time bought the Btc from Binance, Binance took commision from transaction.
or How do you know the seller is Binance robot or real seller ?
questions?
Oh, I see. You think that Binance is selling coins that it does not own or that do not exist. Well, that is possible, it happened with Mt. Gox.
However, if you withdraw the coins to your wallet, then those coins must be legitimate. So, if you doubt them, then simply withdraw the coins.