First, it is very important to understand you requirements .Choose your bike according to your requirements . Check the following things while purchasing the bike .
a) Check all the documents are original and valid .
b) Be careful about the all things are true as told by the owner .
c)Check the breaks, chasis, chain, clutch is working properly .
d) Open the fuel tank and check the corrosion .
e) Check suspension
F) Check average or mileage .
g) Check how much kilometer bike travel(running)
h)Ride the bike .
This things helps you to while buying the bike!