When most of the inquiries are online from sites like Zillow, trulia, etc, the number of responses can be overwhelming. I try to make my first cut by including financial criteria in the ad. It rarely works though. I couldn't possibly call everyone back, so I often send a text thru google voice. I ask them to complete a renter's profile from their site. I then re-iterate the more immediate financial requirements like annual income and move-in amount needed. Also in the text I include a blurb about credit, eviction, and background checks by a paid service. A lot of the responses die off at this point. Those that respond appropriately, I then set up showing appointments or inform them of a Saturday morning 1.5 hr showing. All tours are private so I/we have the opportunity to spend a few minutes with each prospective applicant.
I use the BP app. When an app and signed lease requirement addendum comes in, I follow a similar process as many above. I don't accept any money with the app but accept supporting documents. There is a written list of requirements and most of the information to meet the requirements can be (not) found on the application. Most applicants are discounted at this point. I circle the reason on the requirements list and the missing/disputing info on app. If the person follows up regarding a status, I refer to their requirements list and tell them why they were denied. Reasons have been: requirements state they need xxx to move in, their app states they have only 1/3 of the amount; they've already shared during showing they smoke but yet on app it answer no to the question; previous residence issues.
When they pass my due diligence verifications, I pass it on for the paid services part. The applicants pay the provider directly.