Price really isn't much of an issue, unless were talking $10,000+
Unless your goal is to own a 4910 because it is very nice instrument (it really is) ... With a fraction of that money you could get a farm of LTZ1000 chips and other required precision components. And a nice hobby. And eventually expertise that (if you are lucky) can be used in something which is not a hobby anymore. Just a suggestion.
When buying a 25 years old complex and highly specialized instrument from a surplus source, there is no guarantee that it works properly now or tomorrow or can even be repaired. Whether you pay $100 or $10 000 for it, you still have the same problem.
I contacted the mentioned dealer several years ago. Back then the asking price was 2500 euros if I remember correctly. My question was what their statement "fully tested" actually means and I also asked a few details about their lab. The only answer that I got was that the 4910 outputs were tested with a multimeter.
My point is not to criticize this or any other surplus dealer. I think it is buyers responsibility to ask the simple questions. For example, what kind of lab and personnel it would require to really test the huge variety of special equipment they have for sale. Would it be possible even if it was your lifetime passion in which you spend all your time and money? And finally, would it be a realistic business model (more than a week)?