the reason alot of them smoke is that modern oil can be mix at 40:1, 50:1, and theres even an oil i used that is recomended at 100:1 but the owners manuals say to mix at like 26:1 which with todays oils is way too much and thus causes smoke, also most quad that have self mixing system mix it at a bads ratio.
as far as what too look for:
for $1000 bucks for an 01 if it runs its worth it.
banshee take alot of kicks to start with low comp. so if it starts right up it should be good.
on a side note ill give you $1000.01 for it