NOTE: You cannot bring a rented vehicle, even a UHaul, into Mexico. So, if you were to drive a US plated vehicle to the USA to sell it, scrap it or give it away, you would have to come back to your home in Mexico by bus or plane to buy your car here.
NAFTA agreements on cars seem to apply to importing and exporting manufacturing or dealer organizations, not individuals. Remember, many 'American cars' are actually made in Mexico and Canada. Still, an individual can't simply import one of them to the USA. In fact, there are many models sold in Canada or Mexico which aren't available in the USA and have different content for their own markets. It is complicated and very few expats try to import vehicles from elsewhere. A friend, who had to move back to Florida, just sold his Mexican plated 2004 Nissan Platina and is having to drive his old 1982 Chevrolet guzzler with, failed AC, out of Mexico next week. They plan to abandon it or give it to charity as soon as they get Mexican Customs to remove the sticker and issue the receipt, then cross the border and take a bus from Texas to Florida. They couldn't abandon it in Mexico for fear of the various consequences and the fact that they might want to return one day.

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Read "Streets of Glass" to discover the experience of a retired couple's permanent move to Lake Chapala, Jalisco, Mexico.
PM for details.