Hi Guido, welcome to the forum.
The kapex 120 EB hasn't had an update that I'm aware of since 2012.
I think it's very likely the issue is resolved, but I would definately have the working order of the machine demonstrated to you in person (as with every used tool you want to purchase).
There is no common problem with the 220V motors of the kapex that I'm aware of, (There is however a very common problem with the 110V version, you can do I search on this forum)
The percentages of the price you mention wouldn't be a reasonable price (way to high). But I found the ad on 'marktplaats" , and the asking price is 590, which is 38,6 % of the current retail price in the Netherlands including tax, and 46,7% if you look at the price excluding tax. So I would say it's an ok price.