Sandy has the right idea. Maybe increase the application charge? Has the criteria been updated lately?
Our management company does not use credit scores for qualifications, because the number isn't what matters. The prospects behavior matters, so our qualifications are based on that. We evaluate criminal, eviction, rental history, and unpaid collections. Our criteria is updated usually once or twice a year, to make sure we are in line with our demographic and the ever-changing landlord/tenant/fair housing laws.
What I do is go over the criteria with the prospect first and explain that I don't want to take their money necessarily. I've found that one way to get them to fully read the criteria is to tell them that I am not allowed to interpret it for them, since I do not know their history.
If your requirement is just a credit score, make sure you know what the minimum score is, and let them know they need to check their credit score before they apply. (I use creditKarma.)