Evaluating hubs requires that you already know how to evaluate and adjust hub bearings. If you don't, you can ask a key volunteer or staff member to teach you, but it's something you learn through hands on practice. Once you know how, the process is very simple: evaluating the bearings is the most important part.
[hide] •1 Evaluating the bearings
•2 Flange damage •3 Bent axles •4 Hubs to throw out
Evaluating the bearings
If you feel that the bearings will adjust well enough to make the hub worth being built into a wheel, it is worth keeping. Even if they're not, if the cones are in good shape the hub is worth having around - the cones might be usable as replacements.
If one of the flange holes is ripped, the hub should be kept as parts if its bearings are in good shape.
Hubs with bent axles can also be kept for spare parts.
Hubs to throw out
Pretty much any hub with a steel body is worthless; it won't be used for spare parts, and it won't be built into a wheel. Also worthless is any hub with ruined bearing surfaces, for the same reason.