I wasn't being entirely facetious when I mentioned color. 72s can be galvanized, painted or plastic coated on the outside, or both galvanized and coated. Inside, they may be bare steel or have a plastic or epoxy lining. Galvanized 72s are terrific tanks. Lined ones are not, since the lining tends to conceal and concentrate corrosion, though the lining can be removed if its an otherwise good tank by tumbling or other methods.
Color is one of the best clues to what's underneath. Galvanized tanks will be a dull gray. Yellow are probably the worst, because they are very often USD tanks which were not galvanized underneath and are lined inside. Black, white, blue fall somewhere in the middle since they may or may not be galvanized underneath the color coating, as do some non-USD yellow tanks.
So hard to say whether you got just an OK deal or a steal. If you haven't filled it yet, I'd recommend popping the valve and taking a peek inside. I'd do this with any used tank I didn't buy from a reputable shop. Inspection stickers just don't mean much on eBay tanks.
