Qualifications
It helps to have a background in the restaurant that you're acquiring.
Someone who's been a Domino's deliveryman for years is going to have a leg up in understanding what makes a good pizza franchise work.
You should definitely work at a fast food place at some point in your life so you know what you're getting into.
You'll also need to have a substantial net worth in order to convince someone to sell their franchise to you. For example, Five Guys Burgers and Fries has a $25,000 franchise fee and requires an investment of $153,000-$350,000. But they also want you to have a net worth of over a million dollars (source).
Unless you're sitting on a trust fund, you're going to have to work really hard at some other job to get the cash required to get started on this career. People who are franchise owners are playing the long game.
Not all requirements are as steep, but you'll have to prove that you have enough money to pay for everything to get your restaurant up and running. Plunking down that much cash is a pretty good reason for you to fight to make the franchise successful.
Once you qualify monetarily for a franchise, they'll check out your experience and character to see if you qualify in other ways.
That's right, they don't just give franchises to anybody. Even if you've got all the start-up cash. You're representing their corporate brand, so they have to check you out and approve of you. Buying a franchise is like getting married—you wouldn't want just anyone to take on the family name. What if you're uncouth? What if you have no experience with running a restaurant, and the store totally tanks? And what on earth will the children look like?
Once you check out, you'll also have to go through extensive training from the franchiser that you bought the business from (source).
You will learn exactly how to cook the food, what's in the secret sauce, what the place should look like, and how to handle everything and anything.
Many franchisers will also insist that you go through a trial period, just to make sure you understand the training and are doing everything right.
Opening up a restaurant is hard work, so you're also going to need a lot of stamina and dedication. The hours are long and you'll come home smelling like greasy fries or garlic or whatever it is that you're selling all day. Fish taco shop owners can be exceptionally pungent.