Everybody has explained it already, but basically buyers AND sellers pay fees, you can rebate fees for liquidity makers in v2. v3 may even pay Market Makers more in rebates than they'd pay in fees effectively giving them a revenue stream.

The fees are set in the base currency, in this case BTC as others have said. Stock buyers pay the stock price plus fee. Stock sellers receive BTC less the fee. Stock exchanges work like that. You buy shares you spend $x00 per share plus $y commission. you sell shares you receive $x00 per share less the $y commission.