Taz999:
As another landlord, lemme give you some advice on what you SHOULD be doing from now on:
1. When new phone books come out in your area, don't chuck the old ones. Keep a copy of the old phone book so that you can have all of the phone books in your area accumulated for the past dozen years or so.
That way, when a prospective tenant applies for rent, and tells you where they've been living for the past 4 or 5 years, you can check to see if the information provided is true so that you can know if you're talking to that person's real landlord (or just a close friend claiming to be his former landlord).
2. At your local property tax assessor's office you'll be able to find out the name and address of the people the property tax bill is sent to every year, and that will normally be the registered owners of property. So, if someone gives you a former address where he was living before along with the landlord's name and phone number, pop down to the property tax assessment office and find out who the registered owners of that property are. If it's not the same as that provided on the Application for Rent form, it could be that the property has been sold, but it usually means that the applicant doesn't want you to talk to the real landlord.
3. Most people aren't aware of this, but court matters involving adults become part of the public record. That means that if your local Court has a web site with a search engine, you can search for someone's name to find out if it shows up in any court documents. In this way you can find out if a prospective tenant has had a criminal record (or has been taken to court by a former landlord).
Hope this helps.