FuncleManson
Tele-Holic
Bottom line is human nature. If you're looking to buy, all the sellers are greedy bastards, and if you're trying to sell, all the buyers are cheap bastards. 
Seriously though, I think selling depends a lot on how in need of quick cash you are. I sold a couple of Les Pauls on FB Marketplace this summer. I got full asking price (and $350 more than I paid) on my 2013 Heritage Cherry Burst LP Standard and came down $150 from asking (but still $75 more than I paid) for a 2013 Tobacco Burst LP Signature T. It took a while for both, but I wasn't desperate for money, so I was able to be patient. Someone who needs cash in a hurry doesn't have that luxury.
Seriously though, I think selling depends a lot on how in need of quick cash you are. I sold a couple of Les Pauls on FB Marketplace this summer. I got full asking price (and $350 more than I paid) on my 2013 Heritage Cherry Burst LP Standard and came down $150 from asking (but still $75 more than I paid) for a 2013 Tobacco Burst LP Signature T. It took a while for both, but I wasn't desperate for money, so I was able to be patient. Someone who needs cash in a hurry doesn't have that luxury.