The word qualified does a lot of work in this market. For some suppliers it means the enquirer picked options from a menu. For others it means a person rang them. The gap between those shows up in your close rate rather than on the invoice, which is why the question to ask is which fields were checked by someone other than the enquirer.
What the screen does is remove the clear non starters. Of high income property enquirers we measured, 51.8% fail on finance; on leads cleared by PrimeProof, fewer than 5% do. What it does not do is approve anyone. A broker or a lender does that, with documents in hand. The full list of what is checked is on the page about buyers agent lead generation.