-half started conversions, although buying a bus with the seats already removed probably doesn't count
-full size buses with gas motors, they're underpowered and you'll get like 4 mpg
-newer Internationals (2004+) the motors are junk and they're difficult to repair
-Certain transmissions/rear end combos if you plan on doing alot of highway driving - lots of buses came in really low-geared setups that will redline the motor at highway speeds
-Newer Thomas buses with the Mercedes Benz motors, they're junk (although most of them are too new for the average skoolie to afford yet)
-RUST, run away from rusty buses at all costs. Buy from down South or from salt-free states if possible.
-Overpriced dealer buses, I've seen some crazy markups on buses that were being sold by truck dealers.
-CAT motors, they're expensive to service since the parts are propriatary and can only be bought at CAT suppliers (read: hefty markup).
- rear engine flatnose buses, these are the best for weight distribution and interior space. The rear doghouse also makes a great place to mount a bed
-any buses with the larger engines such as the 8.3 cummins, you'll get more power on the highway and they will be better for towing trailers/getting up the hills
-activity/trip buses with underfloor storage and highway gearing
-buses with rear A/C although this is debatable as oftetimes the factory A/C found in school buses is not very suitable for a conversion