For used panels, i think the standard is Santan Solar. I would have to pay less than the normal rate to drive to a warehouse and pick through panels from someone that wont vouch for the condition or estimated rating. Not saying I wouldn't buy, but i bet they set their prices off Santan. I would offer less and i would multimeter every panel i take outside on a sunny day. If your in knoxville, hit them up. If your going to to drive far, or ship them.. It would have to be a better deal.
https://store.santansolar.com/produc...-solar-panels/