The trader ended up with a worthless counterfeit and a measly 0.5 ETH for his pricey NFT. The scammer quickly flipped the real Mutant for 13.5 ETH, making a tidy $17,500 profit.
The owner of Mutant Ape #21080 was approached with an offer to trade their ape for another Mutant Ape (#55) and an extra 0.5 ETH ($675) to sweeten the deal. The trader agreed, and moved forward with performing the trade on SudoSwap, one of several platforms that allows people to set up NFT-for-NFT swaps. Unfortunately, he didn't check that the "Mutant Ape #55" that the trader was offering was actually the genuine article. The scammer had created a bunch of fake Mutant Apes that look identical through the SudoSwap frontend, but are clearly fakes if you look at the contract.