My local store does 60% of used value. On average. Sometimes it’s a little more. It’s never less.
That can be just fine with me. Convenience has value for me. Not having to deal with tire kickers, low ballers, meeting with strangers or having them over, packing and shipping, are all worth money to me. I can walk into GC any time and get a decent price and walk away. Most of the time the small hit I take from selling to them is totally worth it for my mental health.
Also- they seem to be the only people buying right now. I’ve had stuff listed for weeks on end for VERY reasonable prices. Zero interest. Or I get offered trades for straight up garbage. No, sorry, I don’t want four beat up Squiers, an old PlayStation, and a ten year old iPad for this really nice piece of gear. It’s a tough time to be selling things right now because people just aren’t buying anything.
GC works well for me when I want to get just get things done with no hassle or waiting around. YMMV.

The stuff I've sold to them was stuff I had gotten dirt cheap anyway, so in many cases I ended up actually making money in spite of the 40% cut. As JakeDog says, there absolutely is some value in just getting stuff gone with no hassle, no haggle, or anything. Walk in with some guitars you don't want, walk back out with cash in your pocket about 30 minutes later. Done deal!
Things that make me wonder though:
1) If nobody is buying guitars except GC, are they also paying out all this money for stuff that they're not going to sell for years? Hasn't GC been teetering on bankruptcy or going out of business for like the last two and a half decades?
2) If GC were to suddenly collapse, what would happen to all their used stock? New can possibly go back to the manufacturer, but would we start seeing stacks of 20 Affinity Strats on auctions for pennies on the dollar? Who would want those?
3) Interestingly, every time I've sold or traded in stuff at GC, I've watched for it on their site, or even looked for it in the same store I disposed of it in. Any piece of gear I've handed off went into their back room, and I have NEVER seen it again.