In every year following the sale, the City will reward residents who sell their cars, and do not acquire a new one, with free T passes.
Owning a car is itself a disincentive to own a car, but it doesn't work. People keep owning them. So the City will provide a positive incentive to those who get rid of their cars. At the end of every year following the sale, every resident who is still a resident, and who still does not own a car, will receive a reward from the City: fully funded MBTA passes for the following year. Scammers will be fined twice the value of the reward.
The City will fund this program through aggressive ticketing of moving violations (provided the tickets are distributed even-handedly and without profiling). Owning a car should and must be made more expensive.