They probably already calculated their alternative minimum tax while doing their taxes this year. If they are already paying the AMT then they will get no credit.

But let's say they calculated an AMT of $16,000 but paid actual tax of $18,000. Then conceivably they could get a rebate of as much as $2000 if the vehicle is eligible. The Mariner maximum credit is $1950.

Many states offer additional incentives, you'll have to check in your state. AMT doesn't negate state incentives, to my knowledge.