In the last two years, I sold quite a bit of hgher-end equipment for the window of a friend who passed away. I used both E-Bay and AG. I sold about 70% of the stuff on AG, and the other 30% on E-Bay.
I didn't experience any of the "dishonesty you referred to, but there was more low balling on E-Bay. That is not to say it didn't happen on AG, there just wasn't as many ridiculous offers.
I did my homework via Bluebook, and was fair with pricing, and in the end, got near what I expected. A few items went much higher, a few went much lower, so it all balanced out in the end.
For what it is worth, I've been selling audio equipment (including pro-audio for PA systems), and I've only had one bad experience in the last 10 years. Biggest issue was my complaints fell on deaf ears at E-Bay.
I think you have to be diligent and ask questions of potential buyers, or make your conditions clear ahead of time to deter scammers. That doesn't mean you won't get them, but it makes it easier to sniff them out. Good luck. Hope this helps.

