In hot markets this is a way people often get an advantage as a buyer: tell the selling agent you want to use them as your agent too, so they get the whole 6% if the seller picks your offer. So if the bids end up being close, the agent ends up lobbying for you (or lobbying you to make your offer closer).
Some selling agents refuse to do this because it's pretty shady, but definitely not all.
I've also heard of similar things including negotiating down the selling agent's cut as part of it but haven't seen as much of that firsthand.
