$90, man is that a deal, unless the saw is trashed, that is a really good price!
For me, I'd rebuild it myself, and I'd go over it with a fine tooth comb, even if it needs a new piston and rings, it is still a great deal!
A carb kit does not cost much, but unless you are used to rebuilding carbs, I'd let the shop do it.
I agree, if you put another say $150 into that saw, you will end up with a saw that will run for a very long time!
Check the bar for wear as well, a new bar and chain, with a tune up and you will love that saw!
The pessimist complains about the wind; the optimist expects it to change; the realist adjusts the sails.
William Arthur Ward