My 1st sigma had fungus, it belonged to a pro photographer who must have been a bit thick, he went out in the freezing cold in the winter all day then stored all his camera gear in the ktchen which was very warm and full of steam.
I paid £100 for the lens, sent it back to sigma, I think they charged me £90 to clean it and test it, the lens came back mint and after I sold it I really regretted it.
get a price for cleaning it before you buy it and don't store it with any of your other gear until it's been cleaned, fungus spores spread