Most services in this market take payment first and assess afterwards, if at all. That ordering is profitable and it produces exactly the reputation the whole category now has with property managers.
Putting a free screening first inverts it. People who obviously should not proceed find that out before spending anything, and people who should arrive at the evaluation already knowing what it involves. Both groups are better served, and the second group is the one we want.
It also means the outcome carries some weight. A screening that exists to collect a payment tells you nothing, because it was always going to say yes. One that regularly points people elsewhere is the only kind whose encouragement means anything.