REHAB itself in not a real estate company... it is rather an association of the real-estate service providers. They dont sell properties to people... they bring the sellers to the people by organizing different fairs etc. Since you wont be buying anything directly from REHAB... the trust factor is not really effective here.
Check out these two pages for some more info:
http://www.rehabhousing.com/rehabGlance.do
http://www.rehabhousing.com/faq.do