IBD can be diagnosed with a blood test, or from a liver biopsy. HOWEVER... IBD can NOT be RULED OUT through a clear blood test or even a clear liver biopsy. The vets at UF are very skilled with exotics, which is where I have taken some of my snakes. They explained that the blood or liver might not have any evident inclusion bodies but it could still be present in the brain tissue.. etc.

Personally.. if I gave a health guarentee, it would have a limited duration, such as 10 days or 30 days, etc. If I was given a health guarentee and the snake came up with IBD months later, I would not expect any refund etc, but I would contact the seller to inform them, if I was certain that my snake could not have become infected some other way(i.e. I didn't allow other snakes into the house, didn't take the snake out to other places, etc).

Just my $0.02, hope this helped.