I've never seen codes that make the price go up but I have seen codes that are incompatible with corporate rate codes. For example, Hertz gives an American Expr

I've never seen codes that make the price go up but I have seen codes that are incompatible with corporate rate codes. For example, Hertz gives an American Express corporate rate but sometimes coupons require a different corporate rate (like AAA) and the coupon + new rate is actually a worse deal than just the original corporate rate.