A pre-approval is only useful if you read the rate as carefully as the amount, because a couple of percentage points reshapes what the same car ends up costing you.
Take a vehicle loan of R250 000 over 60 months. At 12,5% a year the instalment works out at roughly R5 624 a month, and you repay about R337 400 in total, of which around R87 400 is interest. Move the identical loan to 15,5% and the instalment climbs to about R6 013, the total to roughly R360 800 and the interest to around R110 800.
The car has not changed. The rate has, and it costs you close to R23 400 over five years. That gap is exactly what a written pre-approval lets you argue about when the dealership's finance desk presents its own offer, because you arrive with a number from a competing credit provider rather than a hope.
Both examples exclude the initiation fee, the monthly service fee and compulsory comprehensive insurance, all of which are capped or governed by the National Credit Act and all of which belong in your affordability sums. Ask every lender for a quotation showing the total cost of credit, and compare those documents rather than the monthly instalment quoted across a desk.