Most declines on a workable deal are not about the customer. They are about the structure landing at the wrong desk. A 2016 Malibu with 20,000 miles, a thousand dollars of negative equity on the trade and $500 down is a fine deal at a lender that allows 115% of book on a nine year old car. Send it to a bank that caps model year 2017 and older at 100% and you get a callback asking for $1,100 more down, if you get a callback at all.
The F&I manager usually knows this. The problem is that fifteen rate sheets change every month and nobody can hold all of them in their head while a customer waits in the chair. So the deal goes to the two or three lenders that bought the last one, look to book drifts, and the rate the customer gets is whatever came back first.