Is this spider worth buying

nothing to worry about but im not 100 percent sure my friend has had his for 4 years and it has a head wobble

"wobble" is a genetic trait apparently passed by the first imported spider. It's not yet known whether the trait can be eliminated, or is tied in with the spider gene itself (much as cinnamons have a pinched snout). The condition may be a minor neurological issue, or it may be an inner ear/balance issue much like that seen in waltzing mice.

A few spiders are heavily affected by the condition, and can have difficulty eating or breeding, but this is rare. Most wobble spiders eat and breed just fine. There's a trend toward acquiring and breeding spiders that do not appear to have the condition in order to try to eliminate it. Some see this as a priority--others, not so much so, particularly since it's not proven that it can be eliminated yet.
At the very least, over time, the trait may be able to be minimized through selective breeding, so that severely affected animals become rare.

If I were looking for a spider and going to pay that much for it I would look for one that was a lot higher quality (better pattern, no spots).