The propositon as framed, sounds all or nothing. You as the seller ultimately control the acceptable offer price. Relative to 100s of calls, that's a demand indicator of property in your market. Often a Selling Agents value is qualifing true buyers, dealing with all the bozos, moving the process towards a speedy close.
A good question for these guys might be, how would you sell my property faster/better/smarter than I'm doing all on my own?