Credit Report

Can any one explain to me how they work. I have done 2 credit checks on myself over 3 years only to the first one show that I had 3 defaults which worked out not to be mine. The other 2 showed no defaults. I'm still trying to get one default fixed. I question is how can they say the default belongs to me when all the person did was have the same name as me. The funny thing this is I don't have anything in my name it is all in the wife's name as I spend a bit of time away from home. I don't want to go into to much details until the police sort it out but would like to know how it works. Do you have to get a credit report done with all credit agency's or should they pick it up that another agency has a default against you. David