Free cat and dog ads can attract those wanting to sell animals to research. If you are uncomfortable asking for money, have them issue a check payable to a non-profit animal welfare organization. Call around and see what each program offers. Most were created for the health and welfare of humans . They were not set up as placement organization.
Some shelters are low-kill.
Some shelters, if no cage space is available, will kill owner-relinquished pets the same day they are turned in. Here in California, the shelters now must hold these pets a minimum of 5 days, thanks to a new law starting January 2000, unless the animal is ill. Some cats are not quick to place and euthanasia is the most humane thing to do. Also, not all pet owners plan ahead allowing for the necessary time to re-home the cat. Cats get disoriented and their immune systems lower leaving them susceptible to deadly feline diseases.