And now I went and explained it. Sorry, tptacek.
If I am selling something and asking $1000 and the person comes back with an offer of $500 and assuming I am willing to take that offer (because I was shooting high) I need to offer some "kickback". This could be as simple as saying something like "well, if I accept can you pay within 5 days?" Or perhaps, "can't do $500 but I'll consider $600". Otherwise the buyer feels perhaps "hmm wow that was to quick and to easy" and might back out of the deal. Strictly my experience over many years.