Most breeders wouldn't sell you a spider if the wobble got bad enough to become detrimental to the snake... especially if it's your first ball. Most spider's have a very mild wobble, and the ones that spin or corkscrew are never really harmed by it. It's really just a quirk more than anything else. My spider's wobble is not mild, though you can definately tell he's got it, but he eats just fine and on schedule, he sheds perfectly, and he's in top health despite the fact that he corkscrews for a few minutes every once in a while (usually after eating or cleaning day like most spideys do).

Don't let it scare you away from getting a spider IMO, they're one of the best morphs out there, and absolutely gorgeous to boot.

But then again, I've never seen an ugly ball python so whatever morph you decide on is going to be pretty awesome.