I negotiate on everything. My all time best haggle was on our house. I haggled over 30k off a spec home and got the builder to take our old house as part of the deal so we didn't have to put it on the market and pay realtor fees.
The developer was in default with the bank but he was also the builder of this particular home and didn't want to lose it to the bank. I went in with an offer of $299,500 and said this is what I'm willing to pay as my only and final offer. He rejected it and countered with what was actually still a really good deal. Our agent pushed us to take it but I'm cheap and stubborn so I declined and told our agent to find us a different house.
A few days later our agent called and said that the builder was willing to try and work something out. He agreed to do a builder trade so he took our old home for less than what it was worth, but because of the cost savings on realtor fees we got about 2k more out of it than we would have accepted.
Here's the best part. The builder was a huge dick and kept trying to get us to do all this work on our old house that didn't need to be done and we almost backed out of the deal but we eventually got him to back down and moved forward. We had to close on our old house first so we could get the money for the down payment on the new house. So three days after we closed on our old house we were still living in it waiting for all the bank transfers to get processed when a major hail storm rolled through. It tore up the roof, messed with the siding, shredded the window screens, etc. Even though we were sill living there the builder had taken ownership three days earlier so all the repairs were on him. We later heard he hadn't insured the house yet after buying it from us which he could do because he came in with a cash offer. So all the storm repairs came out of his pocket. I bet he was all like
while I was like
A few days later we moved into our brand new home and since then the subdivsion has been sold to a new developer who is flush with cash.