Let me suggest a list of information that a potential buyer ought to have before we can fully discuss the merits of a bus.
(conventional, engine and hood stick out in front,
(forward control, engine inside next to driver
(pusher, engine in tail
(van with bus body
(whatnot? There are some rare ones out there
Year of manufacture
(Blue Bird, Thomas, Genesis, Carpenter, Ward, etc)
(Chevy/GMC, Ford, Blue Bird, Thomas, Freightliner, etc)
Fuel used in the engine
(Diesel or gasoline)
(Cummins, Caterpillar, International, etc)
Engine model / size
(5.9, 8.3, DT466, 3208, BT6, ISX, etc)
In addition, determine for certain if the engine has...
(stick or automatic)
(AT545, MT643, 3060, etc)
Number of rows of seats, or number of kids.
(Seats roughly correspond to number of windows. Six kids per full row of seats.
Gross Vehicle Weight Rating – GWVR, found on tag inside. Perhaps same tag as year of manufacture. There may be more than one tag.
Type of wheels
(Do they have a simple circle of lug nuts in the center like on cars, or do they have nuts on top of little wedges of metal out near the edge of the tires?)
Find as many as you can of those. Of course, pictures will quickly answer a number of them.