From my earlier post : "the entire market where this person lives is down 50% from the time they took out the mortgage".

The building they are in was built in late 2005 in downtown San Diego. It doesn't take an appraisal to know that it's underwater - there are many short sales and foreclosures of identical units that can attest to that fact. If anything it's easier for the credit card company to see the mortgage balance then it is for them to see someone's income as that does not go on the credit report.

It's the _balance_ on their mortgage (the amount they owe, not the amount of the mortgage originally) - that is the problem.

Likely the credit card company believes he lives at his billing address, and has done some geo-analysis of credit trends for mortgage holders in his area. Your credit record will indicate when you initiated your mortgage and what the terms were, and it's relatively straightforward to do risk analysis after that.

I've frequently wondered what impact having all my bills sent to Paymybills/Paytrust at Box 14814695, Sioux Falls, South Dakota for the last 10 years has had on my credit profile. :-)