It depends on the tire and age. I always have been able to negotiate a credit for my old tires because I change them at around 50,000 miles. This is usually in the 3-4 year old range. Some places sell the good carcasses to recappers and some sell them as used tires for any use that the customers want to use them on. ON or off road. I have never seen a sign at a shop selling used tires that restricted their use.
I have gotten as much as $150 per tire and as little as $75. My tires are inspected once taken off before the shop gives me the credit to insure that it will serve their purpose, whatever that is.
I should add that you get a higher credit for major brand tires and less for off brand, Korean, or Chinese tires.