Between shipping and fees, I always figured I lost about 8% selling through Reverb. Now that's 10%, which sucks, but still better than selling locally.
Where I live, most guys want everything for free or want to trade their Death Metal pedal for your amplifier. Reverb allows you to get some actual cash out of it.
Having said that I've had good experiences with Reverb, I also wonder whether the company took a bath on the whole "vinyl LP sales" bit. They pushed that for months, not as much now, and they're raising rates.