That new paint might be covering rust in the box wheel wells but a '92 shouldn't have too much rust anywhere else, even in an area where winter salt is used. Like was said above, have a trusted mechanic go over it from one end to the other, oil pressure, compression, front end, u joints (theres 5 in the 4X4) etc. If the dealer has a problem with this, walk, he's hiding something. It cost me $75 to have it done on mine. That $75
saved me at least $3-400, things my mehanic told me that needed doing and the dealer ended up doing for me as part of the purchase price. For reference, in Feb 2000 I paid $8500CDN, about $5500US for my truck with 52K miles on it.

1992 F150 Custom, Supercab SB 4x4 302 AOD 3.55 31x10.5 All Terrain on Ford 15x8 Ralleys