They got a bunch of used instruments in really good condition, and those who sell them give better detail and description than any other market platform like eBay or Amazon.
They're a bit pricey, but they give amazing quality instruments and depending on the offer, they might even hand over some video or book tutorials for how to play.
I use Musicians Friend a lot and their customer support if great. Once because of the gripping cold last year, the drums that I ordered froze and cracked during the delivery. I contacted them and they immediately answered and had a brand new set (along with 2 pairs of sticks free for compensation) within a week!