When I bought my first Car, a fraternity brother of mine was able to get me a GM Friends and Family Discount. He wound up having to get my SSN to give to his Father so that his father could get it put 'in the system'. Which at the time (2006) may or may not have involved others handling that info in the process.
Not gonna lie, if it wasn't for how long I'd known him etc, I would not have believed that GM would use such a thing.
2006 was back when GMAC (now Ally) was the company's biggest profit center. I'm sure they checked credit and made an effort to finance your purchase.
Also, those programs have limits on how many times and how frequently an individual can take advantage of them. They may have used your SSN as the unique identifier to ensure you aren't exceeding the program limits. Not ideal obviously but really not all that unusual.
When I bought my first Car, a fraternity brother of mine was able to get me a GM Friends and Family Discount. He wound up having to get my SSN to give to his Father so that his father could get it put 'in the system'. Which at the time (2006) may or may not have involved others handling that info in the process.
Not gonna lie, if it wasn't for how long I'd known him etc, I would not have believed that GM would use such a thing.