Find a seller that gives you the manufacturer and manufacturer’s part/model number and then find the manufacturer’s datasheet. (And, buy from a reputable dealer so you don’t end-up with a reject or fake.)
The advertised ratings are approximate/nominal. (And that’s from a reputable manufacturer… the specs on eBay may be exaggerated or outright false.) The datasheet should give you the minimum for the particular battery, and that’s what you really want to know.
And, make sure you understand how mA-hr is measured and the test-conditions for the particular battery. It will vary with temperature and discharge rate.