Marie, we really do not recommend the selling of ferrets on Kijiji. You have no clue who is going to take them, what experience that person has, whether or not they can afford vet bills. There have been reports in US of ferrets sold on Kijiji and being used as live snake food and for baiting dogs.
If this is what you feel you must do please visit the home of the person who wants to buy them and check out whether or not they look as if they can afford to keep these animals, are there kids in the house, are there small terrier like dogs? If it is a small home and the owners is a smoker it will affect the health of the ferrets.
Ask yourself, if I had a small baby would I leave it with these people for a day, if the answer is no then do not sell them your ferrets.