 now lets car buyers chop up to $4,000 off the price of a used plug-in hybrid or electric vehicle. It's a speedier way to take advantage of the federal government's tax credit for buying an electrified used car. The credit would otherwise show up on next year's tax refunds. Carvana shoppers must agree to transfer the credit back to the company when they complete their taxes. Eligible cars must sell for less than $25,000 and be more than two years old. Mike Dabusky, ABC News.