Unfortunately when you authorize them to pull your credit, that gives them permission to fire it off to all the lenders they work with. This is very common. Sometimes it pays off in the form of better loan terms. To avoid it, it's usually recommended to secure preapproved financing ahead of time and let them know you'll be using that.
Scorewise, this won't hurt much - the algorithm de-dupes the inquiries and they affect your score as a single pull (loan inquiries are treated this way to avoid unjustified damage to your score since they're all inquiries seeking to secure the same financing). Lenders will still see all of the pulls but the fact that they're clustered in the same day means that for a lender who will recon a denial, you can explain it if they don't discern that these were car inquiries on their own.
As with any other pulls, they'll influence score for exactly 365 days, and will drop off completely 24 months after they appeared (for TU and EQ), and for EX, they'll fall off on the first Saturday of month 25.
