"Slipping" Auto Tranny

I’m taking a look at buying an older Isuzu Trooper. I found an ad for a '94 with 190,000 miles on it that states, “the transmission starts slipping when the transmission gets hot.” Now, like the average Joe, my knowledge of automatic transmissions is limited. So the question is, what do youz guyz think/know the cause is and would it require a tranny rebuild or just some adjustment and fresh fluid? I want to know what I am either getting into or NOT getting into.

190k and slipping, its rebuild time.

transman