Last time I sold, 20 years ago, we negotiated on the commsission. Sellers can pull that in a hot market. We considered using a friend as the agent, he would have sold for 150,000 less than what we got.Early in her career, my wife cut her commission to help the buyer close on a house. I gave her a ton of crap for that. You negotiate on price, not your commission. In the right market, if you're buying, your agent should be working to get you repair credits which are a form of a rebate.
If you really, really want the buy the place, make the sellers agent be your buyers agent. Pretty strong motivation for the agent to nab both sides of the commission. You can also try adding the contingency of "must accept on offer" in your bid.
Tips from my mom-in-law broker/realtor.