You are fishing in the wrong hole here, I think. I would go to a broker.
My bet is that most medallion owners on this site are individual owners, looking for drivers. Most of the corporate medallion holders by now are fleets, and they haven't as yet posted here, nor from what I have heard, want to sell.
In the late seventies and early 80's, when the economy sucked, the owners were paid by commission, 'riding the arm' was rampant, and indivual medallions cost more than corporate medallions, some drivers bought minifleets- I know of one driver who went in on a minifleet with his sister who didn't drive. But that was almost 30 years ago, and many of those guys are now retiring. Still, most of the minifleets are owned by garages, or owners who let the garages manage them.
And they have options. They can either continue to collect the 2000-2200/mo from the garages, or sell the medallion. But with Corporate Prices hitting 650k for garbage Accessible medallions last auction, regular Corporate Medallions are probably worth at least that much. Maybe more, since you figure all cabs now take credit cards, a big competitive boost, and the job market is tight, and there are now 13000 medallions but over 45,000 drivers.
So if you were Jose the Investor, or Sadak the Retiring Driver, or Sammy who inherited the medallion from Grandpa and you wanted to sell, where would you go to ensure the best price? Would you go to www.nycitycab.com to find someone who probably wants to waster your time in trying to lowball you out of a great asset, or would you head straight to the broker who, in this environment, could probably get it sold within a day to garage owner at full market price?
I know what my answer would be.
But Good luck,
Antolin