A lender has many variables to consider when deciding wether or not to stipulate for proof of income on an auto loan:
-If you have comparable past credit they are less likely to stipulate for POI, because you obviously have a history of making a similar payment well.
-LTV ratio, if the LTV ratio is low this poses less risk to the lender and they may be willing to look past POI on the basis of the loan being rather safe in the event of default (ie: buying a car that retails for 20k, for 18k and putting 8k down would make the LTV 50% if based off retail value.)
-Lender's often use data systems such as theworknumber, or other payroll services such as ADP, lender's pay a subscription to these companies, and when the credit application is sent to the lender they will automatically have access to employment/income information which allows them to review/verify date of hire, and YTD income without needing you to physically submit a copy of your POI.
-DTI/PTI limits based on stated income, let's say that your credit application states you are a software developer for google with a stated income of 150k a year, and your PTI/DTI limits are well within guidelines, they can assume based on your job position that you probably, in fact, make that kind of money don't feel the necessity to see it for themselves.
Then you have outlier's like Santander, who often don't stipulate for POI even if many of these condition's aren't met, simply because they are banking on you being able to afford and pay for the loan they give you, with the reward to them being a high ROI in the form of an exceptionally high APR.
My personal opinion on the matter would be, I wish every lender would stipulate for POI on every loan regardless of these factor's, auto loan's are a high risk loan often financed for way too long, with little to no down payment, on a depreciating asset that are prone to mechanical failure. I think lender's are potentially setting people up for failure, without requesting this kind of documentation before extending credit. This of course is just my two cent's, and I am sure there are many people who oppose this.
