[Willyum]

Any used vehicle likely has hidden problems. I have found that MOST of the repair shops don't refill the transmission with Mercon V as recommended by Ford. It DOES cost significanly more for the fluid. I checked with Pep Boys last time I changed mine because their advertised "transmission service" was not much more than the cost of the 7 or 8 qts of Mercon V I usually have to use. The service tech told me they pump it out thru the dipstick hole and refill it with Mercon III. Guy told me that it is "almost the same stuff". At minimum I think the pan should be dropped, thoroughly cleaned and the filter replaced, something Pep Boys didn't include.
Maybe someone knows how this would affect the serviceable life of the transmission but as a used vehicle purchaser you have no way of knowing just how or if ever the transmission was serviced.