I've gotten quotes through a few of these sites in the past, and I was getting at best 50-70% of the value I would have gotten by selling in person through CL. I imagine it's in part because you ship it over to them, they have to inspect the items etc.

I think those services can be useful for buyers, but sellers who want to get the most for their gear will avoid them. Like you said, something like Reverb could compete on taking a smaller cut.