Does it require entering a coupon code? If so, it's a common useless coupon, given to you to trick you into spending more money and earning less. That's because you can only enter one coupon per rental, and so using a $25 coupon precludes you from using a bonus miles/points coupon or any other savings coupon on the same rental.
I get a variety of such coupons as emails from Avis all the time. But since all of them require the use of a coupon code, they're useless to me (since I would always use another coupon anyway), and they're never really great savings.