Welcome to the site !!
Most common is to look for excessive wear , if the seller claims low hours , then the coating on the clutch and ignition covers should not be worn thru , if its heavily worn , then expect the bike to have a lot of time on it
Next would be to look for obvious signs of neglect , like excessive dirt covered in oil , this is a sign of either lack of maintenance or just poor upkeep , which means things will be worn out or on their last leg
Turn the bars and feel if it feels chunky/notchy , if it does then that means it is in need of Steering Head Bearings , not a biggie , just part of normal wear and tear , but its a added expense that should be considered at time of purchase to be included in the cost by way of a price break , this goes for anything that "needs replacing" , including tires , since tires are now in the $200 neighborhood for a front and rear Dunlap , again , a factor as to the asking price
Mainly look for neglect and claims that cant be backed up with receipts , if the owner is not producing receipts for claimed service or repairs , chances are he is not being honest and you could be getting a major repair bill in either parts and/or labor to get the bike up to standards
I am sure others here have suggestions as well that i have forgotten to mention
Hope that helped some
