I haven’t had the pleasure of selling stuff in the US for a while, but my friend sold stuff on Facebook MarketPlace before a move back to Japan.
He said that on multiple occasions, the buyer would agree on a price and arrange an exchange, say $500 for a widget. But then when they met in person they’d be like, I’m not sure I need a widget. How about $250?
I’m not an expert haggler, but my understanding is that it is usually done before agreeing to a price 🙃