I would not even bother if you have a loan already.
This is my issue with FICO scores-no outstanding debt, just (basically) one credit card that gets ~$2-3K charged on it, paid off every month ($9K limit). I have other cards that have around $20K-ish total credit available (but only in an emergency). Causes my credit score to bounce from 790-810 every month! Guess they pay no attention to how much is in the MM, CDs, IRAs,and 401K available to pay them off (factor of 500+ times more). The system rewards people who borrow & live beyond their means…Credit scores are odd ducks if you are debt free. If you are debt free you likely have a single, or maybe a couple of credit cards that you use but pay off each month. If you use that(let's say 1 card) for everything but pay it off, it can impact your credit score by showing you as using a sizeable chunk of your available credit. Depending on when, during the CC billing cycle, they run the credit check, it could show you as using 3K of your available 7.5k of available credit.
Don't know about Canada. But here in the U.S. hard pulls for the same purpose (car loan/mortgages/etc.) pulled close together have very little affect on your credit.I suspect the real reason was that they didn't receive requested follow-up information, such as proof of income.
Just how many hard credit pulls did this dealer hit you with? Too many of those in short order and you'll have a hard time getting approvals.