I would get the tiny one to the vets tomorrow , ferrets can be racing about one min & dead the next, they can hide symptoms of illness untill its to late.
Personally i think the breeder needs a good kicking , i would ring the muppet & let them have both barrells , i hope & prey this little ferret makes it
People make me sick with there got to get rid attitude, if the cretin had fed free rabbit from the off & hung on to them a wee bit longer you wouldnt be having this problem, its so selfish
rabbit caught & froze cost bugger all but time, so no huge feeding