Actually, you need to document all of the conversations in paper. Then present a written request (dated and initialed by you) of your request. Mention the ad, the conversation with said dick, and the 7 day return policy. Cite faulty advertising and incorrect information from said dick. Present the letter to manager, bring a witness, have him video tape it. Be firm with your intent to sue for the value of the vehicle, plus any interest/fees paid for the loan/taxes/title, plus any legal fees. Do this well before the 7 day period is up (like, now, basically). If you live in a small town/city, mention your intent to bring this to the newspaper's attention. The worst you can do is bluff all this...but I'd fight and fight hard.
Oh yeah, and if ABS was so bloody important, why didn't you call mazda with the VIN to verify ABS on that vehicle when you did your carfax?