One of my franchisee clients offered a very simple question that every prospective franchisee should ask of other franchisees when conducting due diligence:

What doesn’t the franchisor do well?

He says this evoked the best responses from franchisees when he conducted his due diligence.  If you are considering a franchise be sure to talk to as many franchisees as possible.  Speaking to only a handful is not enough. 

For more information be sure to read this article on franchise due diligence resources.