If the owner has a clean title and appears trustworthy I would not think twice about it. Sure there is a risk buying used, and buying used for $1,200 increases the risk, but seriously, that is a very low price for a decent running vehicle. I have purchased a few low cost cars over the years when I was a young guy and also helping the kids with their first cars (their money, I helped pick the car). Every one was well worth the money when you considered cost of ownership. Would advise your son to have a maintenance / replacement budget which is appropriate for any vehicle whether $1,200 or $50,000.
Good luck,
Stu