You have to look at the tires often. Mileage isn’t that great of indicator because driving habits and conditions play a huge role. Ask the person when they last changed their tires. Look for a good amount of tread left. A lot of tires have a notch or a line and when the tire wears down that far, it is time to replace them. For my ninja tires average about $100 a piece. This differs from bike to bike based on wheel size and width and how common a tire size it is. I am not saying that there isn’t bad rubber out there but if you stick with a major manufacturer, you should be good.
“I am the best there is at what I do, and what I do ain’t nice.”-Wolverine