Buying a house from a relocation company -- a "relo" -- isn't much different than buying a house from anyone else. A few of the rules are different. In a declining market, though, you may be able to drive a hard bargain.
Find a real estate agent experienced in relocation company-owned properties. If you can't perform a successful search online, contact the major brokerage firms, such as Re/Max, Prudential, Coldwell Banker or whomever you prefer, and ask for an agent with this specialization.
Ask the agent to show you a list of "relo" properties (relo is the trade word for properties owned by relocation companies).
Request the agent to provide you with price opinions (sometimes called a "CMA" for "Comparative Market Analysis") on the property or properties you select.
Write your offer subject to a home inspection by a contractor licensed to perform these.
Seek an attorney to review the documents. Most relocation companies require the use of their sales agreement forms, which differ from standard Realtor-approved forms.