What you want to see in any franchise is a strong positive track record of performance that you can verify during your research. This gives you the security of knowing that lots of other people have gotten a franchise with the company and then done well. If you can't find this sort of track record with any franchise you're researching then find a different one to pursue.
If you would like to receive additional information about all of the many facets you should be investigating with any franchise, you can access the archived articles I've written for Entrepreneur.com over the past 10 years.
You'll find a record of over 100 articles with all the information you'll need to get a very strong idea of everything you'll need to know.