Be sure to get their Uniform Franchise Offering Circular (UFOC)!!! if not familiar with that see this link:
Franchise Registration And Disclosure Guidelines (http://www.nasaa.org/industry___regulatory_resources/uniform_forms/3697.cfm - broken link)
Have your good business
attorney, CPA, and banker all
review it with you along with your business plan.
There is very high risk with a franchise system if they don't do it right.
Buyer Beware... on the flip side, franchising can be a great way for someone to get into business, if the franchisee is legit and will be in business for the long haul.
Do your diligence up front.
If you are new to business it might be worthwhile checking your local SBA office and see if they have a SCORE counselor (retired executives working with SBA to help small businesses - fantastic organization).
SCORE: http://www.score.org/index.html
SBA: http://www.sba.gov/ (broken link)