Not to contradict the tremendous amount of bad reviews, but my experience and purchase with GovPlanet was flawless, so I believe credit should be given where credit is due.
Caveat: I bought through their "Marketplace E", which is a reselling market for similar equipment that you get at regular auction, so maybe processes (or at least personnel) are slightly different, but this is still part of the GovPlanet (or Ritchie Bros) services, and for me this service worked perfectly.
They promptly called me back and advised me of the sellers "left and right limits" (to use a military term), to which I provided what I thought was a very fair bid for the HMMWV, which was promptly accepted by the seller.