Maintenance is key on these. Oil change and filter, air filter, spark plugs, belts, valve adjustment, coolant, brake and clutch fluids. Unless you know the person and have receipts or first hand knowledge just plan on doing all of these things. If the tires are 5 years old or more junk them. Chain and sprockets need to be in good shape. Then you can be sure of your starting point. And start to ride with confidence.