Best methods for handling poli-morphism and MySQL

We use poli-morphism with Java classes and I need to duplicate this with a database design… let me explain…

Lets assume:
– we have customers
– customers can either be rich or poor
– we want to store different details for rich and poor customers; i.e.for poor customers we may want to store information about payment problems, unpaid debt, etc. For rich customers we may want to store details about their assets and buying patterns…
– both rich and poor customers buy products

What is the best design you can think off? We currently use MySQL 5.51.

Thanks

Josh