Whatever boat you buy,you are going to have to take a bit of a risk. Follow most of the advice given here and you will reduce the risk,but not completely eliminate it. With the best will in the world,you cannot crawl over every inch of your prospective purchase,until you actually own it.
In my case,the engine never reached it's operating temperature,investigation found that there was no thermostat fitted.The cooling water pipe to the water filter ( it's canal water cooled) kept getting blocked with weed,and was a pig of a job to clear it.Had to undo the pipe at both ends and shove a curtain rod through it. Investigation revealed that there was no inlet strainer fitted.There were other niggles too that were missed,a leaking window frame,poppers missing from the cratch,and other things that I have forgotten. The point I am trying to make is that untill you have lived with your boat for a year or so,you will not really know what you have got. But don't let this put you off,just offer up a prayer to the appropriate authority,and dive in!