I've sold a few things on Reverb and never had any major issues, but I also photograph well, double check it's working right before shipping, and I pack everything myself. I've never had anything damaged in shipping and never had any major issues as a seller.
I do find it annoying that there is a setting that automatically declines lowball offers but it's fixed at 67%, which is ridiculous to me, because for example if I list something for $1000, there's no way in hell I'm taking $670 - but I also list stuff close to what it is actually worth. I just wish I could customize that auto decline % setting. I also find the current 5% fee to be a bit unfair, considering it used to be 3.5% and they posted record profits even when it was still 3.5%... blame Etsy for this one.
The most annoying thing, and this is the same with any selling platform, are the occasional buyers who harass you. For example, using my $1000 item example above, I've had someone offer $700, so they don't get auto-declined, and when I provide a counter offer for 800 or 850, which is the minimum I'd actually take, they abuse the system and then offer an even lower number like $500 (since that no longer gets auto-declined anymore). I still have to log in and decline that offer otherwise I lose some of my preferred seller score when that really deserves to be left on ignore. I've also had someone pester me to list something from my website for sale via messages on another item for months, and when I finally do, they offer $1000, then decline to pay, and say they'll only pay $900 but only if I sell it "TODAY".... and other stupid games like that. Honestly, the same kind of thing you see on facebook ads and so on. I'm not opposed to having an honest conversation about something I have, or how much something is worth, and so on, but there's always a few outliers that can't be reasoned with. These are few and far between though, at least compared to the overall volume of how much stuff I've sold there.
As for support "siding with the buyer," it's all a very mechanical process, not something against sellers - if you do a shitty job packing something, don't pay for insurance on the package, and it arrives damaged or not working, that is a risk you chose to take as the seller. If you do a good job with the pictures and packaging, not only will you not have any damage to deal with, but if you do, the insurance will cover it and you don't lose anything. The only time Reverb will ever deduct your earnings is if you blatantly send something that is not as pictured, and even then Reverb will still use the insurance part sometimes.
Let me put it this way, I once bought a guitar that had a broken headstock tip that was not pictured or described in the listing. I was pretty pissed when it arrived and rightfully so. I spoke with the seller several times who basically told me to fuck off, so I got a repair quote from a shop, notified reverb, and they gave me a partial refund to cover it, and the scummy seller still got their full payout. If I had bought that guitar through a forum, and the same thing occurred, I would've just reported the issue to paypal and they would've pulled the entire payment, and the seller would've gotten nothing, because Paypal doesn't deal with the idiosyncracies of musical instruments and they don't care - even if I only wanted the repair cost Paypal is not going to get into the mud dealing with that.
As long as you are not out there to rip people off, not trying to overprice items or over-represent something's condition, don't lie about it, and communicate clearly (pictures, description, how long you will take to ship, etc) Reverb is completely safe. I'm not saying it'll be 100% stress free or anything of the sort, nice honest people get ripped all the time, but if you take proactive steps to be a good seller you'll have no issues. Most posts I've read where someone had a problem as the seller, they made an obvious mistake - ex. taking 5 days to ship something when your shop settings say you ship within 2, or not picturing obvious damage, listing something as "like new" because it's pretty but has a functional issue (like a dead fret), opting out of insurance, bad/uninsurable packing job (DO NOT tape together two boxes, I mean come on people), etc. sometimes people who don't sell a lot or are new to it just makes mistakes, and that sucks, but do your homework and you'll be fine.
