There are probably less expensive and more effective ways. My brother was in dispute with a certain BMW/MIni dealer over a second hand mini that burned oil and had multiple faults, it was simply not the well serviced low mileage car that had been represented, he wanted a full refund, did not want the car , but they refused to take it back.
He had large vinyl posters made for all the panels and windows identifying what the problems were, put the car on a trailer and parked in front of their showroom (in their car park) early on a busy Saturday. He sat there drinking a flask of coffee as the sales staff looked on horrified, told them he was there for the day, the next day, and the next if necessary..
After an hour or so the police turned up, but the officer said it was at worst trespass, and was a civil matter, nothing he could do except keep the peace. Another hour or so and the manager was out there offering the full refund...
Result: He and his wife would never touch a mini or that dealership, even if they were giving cars away, and everyone that drove past that day will remember it, and hopefully drive past next time they are looking for a car!