Audio solutions Indy is a great place. Their prices are a little high, but the staff is highly knowledgeable and they have more inventory than the other 8 audio stores within 150 miles of me combined. Like 20-30 times the inventory New/used I have seen anywhere. I stop in once a month or so and it takes hours just to look at what they have.
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.