I'm selling a 20lb propane tank that is full, almost completely. I purchased it a few years back, never bought a grill, and it stayed outside under outside porch roof. The day I bought it I decided to top it off at Uhaul. Based on my math it has a tad bit over 4.5 gallons of propane.
The knob turns smooth, the tank has some slight rust spots here and there, but solid overall. date stamped 11/2020
Full 20lb tanks can go for over $65-$70, send me a reasonable offer and maybe i'll consider.