Hey Marko,
I have a 1972 CB500 Four. I don't believe 52000Km is too much as long as the bike has been well maintained.
Do you know what an original 500 looks like? This is important because you will be able to spot any modifications, like exhaust, tank etc..
I would still suggest you do the following things:
1) Compression test, doesn't take long and it is a good indicator of engine health.
2) Ask when the points, valves, timing has been checked. If he doesn't know, this is not good. By listening to the bike run, you can determine if these things were done.
3) has the bike been run regularly over the years. If not you may have issues with the carbs, they are quite sensitive to old gas, dirt etc.
4) Take a close look at the gas tank, especially at the seams towards the back, if you see blisters this indicates rust and may cause leaks in the near future. Also, open the tank and look inside, it should be reasonably clean without much rust.
5) Start the bike when the engine is cold, these bikes are notorious for cold starts. If the engine is warm when you get there, be suspicious.
5) Test all switches and electronics, don't assume they work. The easiest way is to start the bike, try all lights, signal lights, brake lights etc..
6) Check the drivetrain, chain and sprockets and of course check tires for unusual wear or cracks.
7) Check exhaust for leaks or holes, easiest done when bike is running. Original exhaust pipes for these bikes are expensive to replace.
In the end, you can't expect a new bike but 900 Euros is a good price if the bike is in decent shape and well maintained.
Hope this helps,
Claude
