File: DutchTrade.sol
257:         uint256 balanceBefore = buy.balanceOf(address(this)); // {qBuyTok}
258:         IDutchTradeCallee(bidder).dutchTradeCallback(address(buy), amountIn, data);
259:         require(
260:             amountIn <= buy.balanceOf(address(this)) - balanceBefore,
261:             "insufficient buy tokens"
262:         );
