This is how it worked, in a nut shell. He went around to some local car maintenance garages and got them to agree to give a free oil change to anyone presenting his coupons. (Limited to one, per customer, per month or something like that.) When he got 10 or so garages to agree to this, he had professional coupons made up that gave the bearer 10 free oil changes, spelling out the redemption terms… etc.
He sold these coupons for $60 to people door-to-door. The customers were getting a great deal since 10 oil changes will cost you at least $250 in most places. He got to pocket this entire amount. His only overhead was the cost of printing the coupons and paying his sales people that went door-to-door for him.