That was our problem and why we started to think about charging one. We are just a family business but manage and own 125 units and for a our last vacancy we had over 15 applicants apply and a Bunch were just crappy applicants. We are looking in the neighborhood 10-20 for the application fee.Application fees are becoming the "norm".
Consider the amount of time you as a landlord invest in a potential renter. Do you work for free?
Keep it reasonable, but make it clear up front why you're charging it and what it's for. It may also help weed out undesirable tenants.