Okay, firstly you obviously know a bit about cars, so look on the car sale websites and compare the current sale prices to see if they are close to the same as the 03 R1.
Next when checking out his bike, look at how worn the tyres are to the edge of the tyre, if they're on the edge, it means he rides it hard. Feel the forks, if they're smooth with no oil leaks, all good. Feel the brakes for soft spots, so wheel the bike and slowly apply the brakes, to check if they have been warn. Then just look for general wear and tear and make sure the brake fluid, oil, etc is all a good level, if so, then you have got a perfect catch!