Missing items on your application: what you don't know can hurt you.
You have done your homework and carefully added extra questions to your Application Form. You made sure you were getting adequate residence information, full employment details and covering all the bases in credit and identification. What does it mean when the Applicant leaves some of these answers blank? It may be laziness, lack of concern, poor eyesight, and ignorance of what you were asking for or just about anything else you can imagine. The key point isn't why. Just know it isn't good for you and your organization.
Frequently the Applicant doesn't want you to know something. That could never be good. It is important that you review your application before the Applicant leaves and make sure ALL the spaces are completed. If the Applicant says they don't know the answer, have them make a call or look it up on the internet. If they say they can't do that, throw out the application. It will cause you more trouble than it is worth. You cannot verify most employment information unless you can provide it for the Employer. They will let you know if the information provided is accurate but won't join you in a fishing trip for salary, length of hire or current hire status.
You can obtain Credit information with a social security number, but, without confirmation of address and complete name information you will never be sure if that report really belongs to the Applicant. The same is true for employment verification. You can ask if Bob Jones works there but you need to know the Applicant is the same Bob Jones and not your Applicant's Father. If you can't verify salary you haven't learned much. Perhaps the income is far too small for your requirements.
If you don't get a full current address you may have problems verifying information linked to the previous addresses you find in the Credit report. This could include eviction or criminal activity. Like I said, none of this is good. You work hard to make a living and you don't want to spend needless money and energy chasing down a customer who owes you money and who you don't really know. The best way to do this is to make sure the complete application is filled out and it is all verified.
A completed Application does not guarantee you won't lose money any more than an incomplete Application guarantees you will lose money. Most of the time, it just seems that way.