Nothing is less legitimate than a domain brokerage service that conveys offers to buy domain names without applying the slighest intelligence to the process.
I have received more than a few inquiries from NetSol and GoDaddy and, in every case, "the service" merely acted as a communication agent - forwarding the interested party's offer. AFAIK, given the disconnect between the "offer" and the quality of the domain, no one actually evaluates the offer to determine if the offer should even be communicated.
Dear Domain Brokerage Services: MAYBE, for your fee, you can offer advise to interested parties to make offers other than "offer $500" or "increase your offer to a $1000". Unfortunately, that's as far as I can tell the advice must go.
So, having established that their "domain offer" services are no better than the random nonsense inquiries I get in my email inbox every week, I have put their services on my filter list -> spam, trash, nonsense.
It's a shame. IF any ONE of them applied just a wee bit of intelligence they might be able to CORNER THE MARKET on the "we will act as you anonymous intermediary for low end ($5K-$15K) deals".