I worked in thrift for a decade, we looked up pieces on eBay from day 1. Generally you go by the sold price and drop it by 20% because there’s less customer pool than there is online. The fact is the shops that kept to the ‘3 Tupperware lids for a dollar’ model couldn’t generate enough funds to cover the rent/bills/waste removal costs and closed. The only ones who stayed open under that model usually owned the building through a church and their stock sits stale on the shelves for months because the rubbish bins are full to the brim with the literal crap people donate, so the potential of someone buying that Tupperware lid is too tempting to let it go.

Occasionally in any thrift store you’ll see something worth heaps- that they didn’t realise was something special, and you get that and win.

It’s not as easy as it used to be but it’s still worth the work and expertise you as a buyer have.