I did a trade-in deal with TMR a few years ago. They gave me a very fair trade price for a Bryston B-100sst towards a Primaluna Dialogue Premium. The tube cage of the PL came in with a cracked glass and they replaced the whole cage within a week. Very satisfied customer.
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.