[pcthrowaway]

You can set a slippage tolerance when you make an order on a decentralized exchange. It's basically the same as a limit order priced to market, where you effectively set the "most you're willing to buy for" / "least you're willing to sell for" and occasionally get better rates.

With a DEX your transaction might just not execute at all some of the time of creating the transaction, so you might burn a transaction, and there's no orderbook for the order to sit in til later.