The primary benefit is cost savings. You can often find high-quality, solid wood furniture for a fraction of the price of new, low-quality particle board furniture [1].
"I love that I can find unique, vintage pieces for my home that have a story. It's much more interesting than shopping at a big-box store." - Common consumer sentiment [1]
You can usually get a decent return on your furniture, especially if it is in good condition, while still offering a bargain to the buyer.
"Selling on Facebook Marketplace was fast, but you have to deal with a lot of people asking 'is this still available?' and trying to negotiate the price down." - Common user experience [2]