Im going to check out this TH350 that this guy has in the paper local to me... its a TH350 with shiftkit and highstall...

i will take it to a shop... but what should i look for, so i don't waste my time.

First smell the fluid, if it smells toasty, pass. Pull the pan, anything other than a light dusting of bronze thrust surface material and some clutch dust,, pass. If there is any aluminum dust in the pan, pass. If the pan has been recently wiped squeeky clean, pass, he's hideing something.
If there is trash in the trans, it is also in the convertor and short of cutting it open, you have no idea what you got. It's always a good idea to have the convertor drilled, drained, flushed and a drain plug added so future fluid changes will change more than just the few quarts that are in the pan. I don't mean to sound like a pesimist, but buying a used automatic / convertor is always risky. You just never know exactly what your getting. Myself I look at it as a core, and plan on going through it cutting the drums for more clutches, freshening the thrust surfaces,,, and a 'high stall convertor' could mean anything from a $99 convertor to a $400+ custom piece. Ask for receipts if the convertor is a major part of the price. On your way to look at the trans, stop at a trans shop and ask what a core will cost. Might help make the decision.

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