Dealers That Sell Large Volumes of Used Gear Online


I have purchased from a couple such dealers, and my favorite so far is The Music Room in Colorado.  They have been entirely professional, and most importantly, their gear always arrives well packed and in better shape than even their description would lead one to expect.  Their prices are reasonable, they are not gouging. I'm not affiliated, just a happy 2x customer.
peter_s
I've had straightforward and fair deals with both Perrotta Consulting and Weinhart Design, although not as good prices as TMR (still, it was my choice to do the deal). Luke warm to cold experience with Scott Walker Audio, who ultimately didn't have time enough to fix a problem and was too busy to respond with reasonable promptness. 
Underwood Wally is a straight shooter...  you just need to know what you want. 
TMR has very good customer service, knowledgable and respectful. And very reasonable prices for a dealer.
Underwood is good, many nice items, but I don’t like the no return policy. Even on a close-out, there should be a return on some items.
I asked TMR if a speaker was finished in real wood or vinyl, they told me to write down the serial numbers and call the manufacturer...I was done with them...
Underwood — Several purchases, always happy about the price and product (multiple PS Audio PowerPlants).

HigherFI — One very happy purchase (Avalon Eidolon).

USA Tube Audio — Good deals on Ayon gear (Triton III, CD07)