electric start = pusswah, kick it or buy an enduro! Electric start is NOT cheap to do, there is now place for an electric starter motor etc etc.

After buying a fair share of bikes myself here's what I'd look for:
- Any oil buildup on the engine cases (gasket is leaking if so) Its not a HUGE deal but if its spotless then that's a better sign

- Pull the dipstick or look in the sight window, that oil better be like caramel, if it is black beware.

- Check the radiator out and make sure the water looks clean and green

- Sit on it and hold the front brake and rock it back and forth. Suspension shouldnt be 'sticky' and look at the front forks for oil seal leakage.

- Look at the chain/sprockets, no pointy teeth, chain slapping the swing arm, etc etc.

- Crank it and listen to the top end. If the valves are way out of adjustment itll sound like elves beating the engine from the inside Not sure how noisy the CRF's are though, you will probably hear the valves ticking though but it shouldnt be heard over a revving engines exhaust.

- Apply what Wolfey said as well...

- Take a look at the air cleaner, is it packed full of narsty or is it freshly clean and oily?

- and i plus one on the racing factor, if it is raced yes it's ridden hard (like it was built to do), but MOST racers meticulously clean their machines and keep them in top shape. Weekend warriors have a bad habit of going out riding and then parking the bike for a while w/o then pulling maintenance. The racer takes his bike out twice a week in front of hundreds of people, you dont wanna be that guy riding a ratty pos at the races