Do you gather more personal information progressively?
Most people don't like to disclose personal information and in some cases will give you dud data. This is more often the case when people are required to give a lot of information at one time. What we have found at SSW is that you will get better quality personal information at intervals and not all at once.
For example: Lets say I go to a website to download some software, but to do this the company requires me to give my Name, Address, Phone Numbers & email address. The likelihood of them receiving my correct details are limited as I don't know what they will do with these details and I don't know the company at all. However, if that same company only asked me for my user name and email address only I would be more inclined to leave them the correct information as this is not as intrusive and a lot quicker. I would also be more inclined to go back to that website and download more, which is when you ask the user for that little bit more information.
The second time round that company may ask me for my real name and a phone number. Again this is not as daunting because as the user I have already given this company some of my information and feel that I can trust them a bit more than the average company.
The third time I go to download they ask me for a little bit more information, so by the time I have visited their site to download I have effectively given that company all my personal information.
Of course this does not guarantee that people will cease inputting dud data, it does decrease the chances though!