I couldn't imagine selling a horse with wobblers, much less buy one. I'm going through this with my yearling right now...he hasn't been diagnosed as "wobblers" but he's grade 4/5 neurological, presents as a wobblers horse would, and dangerous to be around. This is due to what we believe is a compressed vertebrae at C-6 but we now believe this was preceded by a genetic condition. Can't transport him to find out more due to his instability. He really doesn't understand where any of his four feet are, though he is gaining better control of his front feet. Tonight was the first night in a month I've been able to even pick his feet during which he did have quite a loss of balance. He's a danger to himself right now and a danger to anyone who enters his stall. And he's not even 15 hands and 1000lbs at this point. Of course, however, his condition is much more serious than a wobbler which one would consider riding.
Because I already own this horse I will work around him very, very carefully. He's my dream horse, my heart horse who was supposed to be my next FEI partner. So I will do everything I can to get him pasture sound and keep him with me. However, any time I am near him I'm aware that I'm risking my life. Even a more mildly neurological horse (say a 2/5) may very well trip and fall due to a slight lump or dip in footing. A small slip because of ice or mud will certainly more easily cause a tumble. These horses do not have normal control over their limbs making them a risk to riders and handlers. I couldn't imagine climbing on top of one. There are so many wonderful, normal horses that need homes, to buy one with this issue (which other pointed out may even become progressively worse) seems like a poor decision. I'm glad to hear you've decided that this would not be a good idea.
Some people will ride horses with wobblers but the specialists in the condition suggest the horse should be a grade one or less, so a virtually normal horse. Even then, I wouldn't buy one with the condition. If my horse, whom i've already owned, was diagnosed with wobblers and recovered to be a 1 or less I MAY consider riding on a level surface with excellent footing...but key word is MAY...not sure that I could convince myself that it is worth the risk.
If you (or anyone else) are interested in learning more about wobblers, google Dr. Barrie Grant. He is a pioneer surgeon for the condition and has a very informative, comprehensive website. However, after talking with my local vets I personally believe that Grant's website describes the surgery in a much more positive and successful manner than it realistically is. Still, provides very interesting information.
Anyways, that's my 2 cents (or 5, maybe at this point lol).