What to look for when buying a used optic?

[Bridgebuilder34]

I’m possibly going to be buying a used spotting scope tomorrow. What do I look for besides obvious damage? I’ll be able to inspect in person.

 

[gr8fuldoug]

Shine a flashlight through, both ends, and look for clouding, specks & fungus

 

[moosemeat]

Lifetime warranty.