I don't really mind the fungus, stiff focus or sticky aperture assuming that the seller warned about the problems. What drives me to despair is when the lens has clearly been fiddled about with by someone who didn't have a clue what they were doing. I've even found greasy fingerprints on internal elements before now (after noticing that the front element group wasn't screwed in properly and investigating further).

My repaired lenses are usually capable of very decent results, inevitably they end up with a little fine dust in as there's no way to avoid this without a clean room and moonsuit. But no fingerprints or smears. I keep meaning to go back to one of my first major projects (Pentax 28-50mm riddled with fungus) and see if I can get it a bit less dusty. It's not bad, but could be better. Also noticed a tiny speck of cotton or something in there, amazingly it still takes perfectly good photos!