I've sold about 20 items on Reverb over the last two months or so.
Since I live in Belgium, it's an easy way to find a 'broader audience' than on a local 2nd hand website.
I've encountered no problem at all, but might have been lucky of course. Each item (guitars, pedals, amps) sold within a couple of days or maybe a week at most.
One nice feature when selling was the 'market price indicator' based on past transactions on the website.