well for efty, the new templates have make offer only (with minimum bid if you want) or make offer and buy now, or I think just Buy Now.
if the buyer chooses to make an offer it comes to your email and you negotiate and finalize however you agree.
if they choose buy now, same thing, unless you choose escrow integration option, it goes straight to escrow as far as I know.
Undeveloped it's a private chat window within the site where you negotiate with the client.
but in both cases nobody negotiates for you unless maybe you have very very high value names in which case I'm sure if you reach management, it would be in their favor to help. Domain Name Sales not 100% sure how it works.