The problem with headsets is that they are under forces (amount, and more importantly the direction those forces are coming from) that the bearing surfaces are not great at dealing with. And so, it is not at all uncommon to find older headsets to have comprimised bearing surfaces.

If the headset uses cartridge bearings, then simply replacing the cartridges will pretty much give you a new headset. In the case of loose bearing types, if the races are in good shape, then they are certainly useable.

I would be reluctant to buy a used loose-bearing headset that I could not inspect first. And since decent new ones are readily available, it seems to be a unnecessary risk to buy a used one off Ebay. With a cartridge headset (King, or otherwise), then as long as you factor in the cost of new cartridges, then no problem.

jim