This article is from the Australia Motorcycles FAQ, by Cameron Simpson cs@zip.com.au with numerous contributions by others.
Consider the kilometers the bike has travelled. Look for oil leaks,
especially in the lower gaskets (the joins between the pieces of the
engine and gear cases). Look for signs of crash damage or racing use
(eg oil caps and the like with small holes drilled in them to
accomodate "race wire" used to ensure the bikes stay done up and with
the bike). In a learner bike race use is uncommon.
If you're getting serious about a bike, make sure a friend test rides
it. Try to check you're buyng from the bike's real owner: do the rego
papers match the address you're at, does the seller's licence match
the owner on the rego papers, do the rego papers match the bike
(plate, chassis and frame numbers)?
Before you buy a bike, do a REVS check. This is the Register of
Encumbered Vehicles. It lists bikes with money owning on them; such
vehicles can be repossessed. You can do a REVS check online here:
Register of Encumbered Vehicles
http://www.revs.nsw.gov.au/
 
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