I turned down a $15000 offer from Amazon for a 2 generic word .com domain hand registered in 2019 and sold it to them two weeks later for $25000 USD. The Uni broker asked me to take the $15k because the buyer is losing interest, but I told him to close the inquiry and I walked out of the negotiation. I followed up 2 weeks later and the sale was completed at 25k.
Make your research, understand your buyer, stay firm but yet flexible