Some of our clients have subscribed to widely published Internet databases and search sites offering to locate someone for a very minimal flat rate. Although I would not say that this is always a bad idea, you might want to be careful about using the information and results that are returned. Some of these databases just pool information and offer very little in the way of filtering or verification. You are left with the raw data. If you have a common spelling on an individual's name, there is a likelihood that you will get results at absolutely nothing to do with the person you're looking for. Most private investigators are able to take this raw data and go one step further with either other databases or other sources and verify the information. This is the reason that private investigators don't always charge a flat rate of $39.95 to locate someone. Nowadays, anyone with a credit card can access some of these sites. Be careful about relying on the information provided without doing some sort of additional verification.
A good private investigator will utilize multiple sources to verify information. When they present something to a client, it will be presented in a context that conveys how confident the private investigator is with the veracity of the information. The bottom line is, if I'm not 100% certain of the information I just tell my client that I believe that it may be correct, but could use some additional verification.
There is really no magic formula that a good private investigator uses to access information. Most often, it is because the investigator has established contacts or resources that have come through years of work in the field. What may take another, untrained, person several hours to find may take a private investigator a half-hour.