My question involves vehicle registration or title in the state of: Oregon

My 16 year old son worked all summer to save money to buy a car. He found one on Craigslist that would fit in his price range of $3000. He and my husband test drove it and it was obvious that some after market work had been done to the car to improve it. I asked the seller straight up whether the car would pass DEQ and be able to be registered in Oregon. He said, "no problem", (of course). We bought the car with cash. A few weeks later, we took it in to the DEQ and it did not pass due to the car computer not "speaking" to the DEQ computer. We took it in to a mechanic and he said it looked like the wrong engine was put in the car, and to take it to VW mechanic. We found out today that the car will never pass DEQ, and we should just sell it as a "mechanic special." In this case, we would not get the money back that my son had worked so hard for. I am very upset about this- especially for my son to buy a first car he can't even use. He is so disappointed.

I know that Craigslist sales are always cautioned, but is there anything we can do legally- since the seller knowingly sold us a car that can't pass DEQ? Do we have ANY recourse? What advice do you have?

Thank you in advance for your help on this.