If you were buying a car, settled on the price, and then seller told you that in addition to the 40,000 miles on the odometer the car was also towed across the country for an additional 40,000 miles would you think you got a steal of a deal or would you want to either walk away or negotiate a much lower price?
I am not a lawyer, but if I bought a used car, had suspension trouble shortly thereafter and found out that the car had be towed for 40,000 undisclosed miles, I would think a legal action might be warranted. The fact the car is a tow car is a big negative to most people. I personally would disclose that fact and have it signed by the buyer and expect to have to discount the car to make it go away. But I err on the side of caution.