The family business was an enormous Mobil franchise that peaked at about 20-something servos across NSW.
Things that I observed in the time I spent in a management role there in my late teen years were:
1. Massive entry cost, so you'd have to bring some wealth, you can't start it from scratch.
2. Hands in your pockets - The formulas for franchise fees were, in my opinion, too complicated and there will be a constant power struggle to keep the franchisor out of your pockets when they want to audit, play with numbers, renegotiate, etc. I think that this was especially bad in the servo industry where there would two agreements running in parrallel - shop and petrol volume.
3. Conforming - Constant, pointless evaluation to ensure the place looked clean, which always resulted in useless negotiation about branding and entitlements. As you may recall, when Mobil introduced synergy (8000 98 octane etc), it was only supplied to certain sites that could comply with a "criteria" which meant some were left behind and today look in a state of some decay.
4. You are at the whim of the franchisor - If they cock it up, then it will hurt you. Woolworths originally approached Mobil to set up the discounting regime and for some reason they declined. You may own a business, you may operate it, but don't think that you will ever truly run it and give it direction, someone else is steering that ship. If you wanted a particular site, they would only give it to you on the condition of taking on another loss making site.
My final thoughts from my experience are that if you are going to enter into a franchise agreement, you have to do it on a large scale to be successful (i.e. as many sites as you can). Servos were a commission based game, so it was all about pushing volume which meant going big on picking up franchises. Getting in to just one of any franchise is difficult because its likely that there is someone who is building a web of their own in an area. If you have the resources to do it on a large scale, then you will be successful, if you don't, then I think that it will be a struggle.
As someone has already said, its much better for your happiness and wealth to be a franchisor.