ThredUp, Mercari, and Poshmark are my go-to’s right now. If theres something specific im looking for, sometimes eBay. There’s secondhand sites like DePop and Vinted that offer more specialty vintage items, and then other sites that offer secondhand luxury/designer.

Oh and if you get into thrifting make sure you get a de-piller. They take off all the little clothing nubs and make stuff look new.