What if a buyer has insufficient tax liability to fully use a transferred credit? (added October 6, 2023)

A4. The amount of the credit that the electing taxpayer elects to transfer to the eligible entity may exceed the electing taxpayer's regular tax liability for the taxable year in which the sale occurs, and the excess, if any, is not subject to recapture from the dealer or the buyer.

Hi to all, today IRS added some new to FAQs on its website. My question is how seller can find out taxpayer tax liability while he/she did not file tax return if wants to take this credit at the point of sell in dealership? And how we can figure out client already used this credit in the dealership?