I just bought a used EV and was able to take advantage of the credit. You can use either last year's or this year's taxes. Whichever is lower. In my case, we were below last year but will be well above $150k this year. So we used last year's. I didn't have to show the dealership anything. They gave me a checklist and I had to certify that I met every requirement on the checklist.

The credit is great and lowered a $20k car to $16k. Because used EVs are already very depreciated, this was a killer deal.

MY understanding is that you may immediately assign the $4K credit to the dealer to apply toward the purchase price. Then you need to file paperwork with your tax returns the next year to keep the credit or the IRS will charge you for the $4K credit. So you don't need to prove your income to the dealer, but will be charged the credit if you end up not qualifying or otherwise failing to correctly submit your taxes forms.

I am tempted to get a used EV. My AGI last year for 2023 was just over the $150k married filing jointly limit. This year we should be under the limit for 2024 taxes. If I want to get the car this year, what does the car finance office need to see? Can I compare paystubs from last year his year to show we are on track to be below the $150k limit? Or do we need to wait until January to show final AGI shown on 1040 tax forms?
Thanks for any input.