Is 4 hairballs in 11 days a bad sign for a ferret?

Ferrets do not throw up hairballs like cats, they have to process them. A laxative or even some petroleum jelly will fix that. If the ferret has a dry cough that you hear frequently, it probably has a hairball. Just give it some of the laxative for a few days and it should be fine. I have 13 ferrets and do not have to give them a laxative very often at all. I don't ever see hair in their poop, so I wouldn't worry. As long as the poop looks good and the cough doesn't sound wet, I wouldn't worry about it.