Why does everyone think their second hand stuff is worth more $$$ than it should be?

First post so apologies if the formatting is off.

I can’t figure out why everyone thinks their second hand items are worth so much. I regularly will look on marketplace or trade me to see if there are any good deals for myself or to send to friends who are looking for specific things e.g. couches. I cant believe how much people expect to get for their secondhand items that are in pretty poor condition (stained, torn, sagging, faded etc). I understand one would want to make as much $$$ as possible from their sale, but I just feel that what a lot of people are asking is unrealistic.

Does anyone else feel this way, or do I just have unrealistic expectations?