Although ferrets have superb fur coats and are remarkably well insulated against the cold (they are related to mink and otters) they don’t object to being dressed up. The practise seems to be common  in the USA. Personally I don’t dress my ferrets, as it is unneeded,  but some have other opinions.
Shown is beefy (looking like a sausage roll) modelling a ferret knitted sweater by Sally Rhymes, who also knits sleeping sacks for ferrets  and sweaters for dogs.
Ferrets are good natured and tolerant creatures, as can be seen.
Sally will also knit ferret sleeping sacks, as illustrated, ferrets like a snug bed. Useful for ferrets kept indoors, and the infirm or elderly.