As the owner of a headshaker, I would never recommend someone knowingly purchase one, unless you are willing to deal with what can be (but isn’t always) a very debilitating condition.
The condition can be difficult, if not impossible, to manage and what works for one horse may do nothing for another. There are so many different possible triggers and treatment that its can be overwhelming trying to figure out how best to help the horse. Some can benefit from a change of location (if it’s allergy-related, for instance), some can be helped with meds (although if you show, the meds are usually not show-legal) and sometimes, no matter what you do, nothing works. Unfortunately, with nerve-based pain, medication really doesn’t do any good, you mostly just have to try to prevent it from starting.
My gelding is a homebred and he started last spring at eight years old, completely out of the blue. I’m still trying to figure him out and what works best for him, and it’s heartbreaking to watch him when he’s having tics. When he started, I immediately had to accept that he may never show again. In my case, my horses live at home so I have the option of retiring him at such a young age. If you board, you have to consider that it would be very, very hard to sell this horse in the future and that if you do, he may end up with someone who doesn’t understand the condition and how to deal with it and be able to accept that he may not have a happy ending.
Do some internet searching – there’s a Yahoo web board with tons of good information and people willing to share their experience. Tons of info is out there, you just have to sort through the snake-oil salesmen and those with real information to give. But to be blunt, if someone asked me if I would buy a headshaker, my answer would be “no”.