If you are serious about a particular franchise opportunity, you will be given a copy of the Uniform Offering Circular (UFOC), which contains financial and other important information about the franchisor.
When reviewing the UFOC, make sure the franchisor doesn't have a high litigation record, its franchise outlets are performing well, and it adequately protects its intellectual rights. If these rights are not properly protected, other businesses could profit from the name recognition you paid to use.