You know that old saw about "it is impossible to make things foolproof because fools are so ingenious"? Trust me, you will be amazed at how "creative" the DIYer can be with anything you put in their hands.
Like Greg said, it can be a lot of fun - for a while. People ARE different now then back in the 1970's. Insurance IS different now than back in the 1070's. Peoples expectations are different now than in the 1970's.
Like Paul said - it takes a lot of your time. You will need an employee who does very little else other than babysit. If you are going to be the one to be doing the babysitting, figure you are going to be doing your custom work at some other time - usually after the shop is closed and on the weekend.
Like Bill Henry said - it is kind of therapy for your customer. You have to decide if giving therapy away for free will pay the bills.
You have to have the personality for this. You have to have patience and tact. You have to enjoy teaching, showing, and interacting with a learning public. You have to be enthusiastic. You should have some first aid skills (accidents do happen). You will probably want to decide what kinds of projects you will allow customers to do, and how large a frame size you think they can handle. You have to not mind repeating the same thing many times over, day after day after day after day . . . .. .
There's not a lot of money in it. Shops that offer/offered it in my area reduced the price by the fitting charge (anywhere from 10 - 20%), or charged a table charge or a per picture charge. None of us promote it, or offer it anymore.
Michaels/Aaron Brothers offers FREE framing if you buy a ready made frame from them - you can DIY at Michaels or you can have them frame it for FREE! Which do you think most customers choose?
Best DIY customer I ever had? A blind man who listened to my directions carefully, worked moderately, asked questions if he didn't understand something BEFORE he did anything, and allowed himself the necessary time to do the work. He was very good at DIY - and better than some sighted framers.
Worst DIY customer I ever had? The society mother who handed me her sick toddler to "babysit" while she tried to frame a picture for a function with less than 45 minutes before it had to be presented - including driving time to the event. She was so busy talking on her phone, ignoring her baby and my directions as I helped another customer that she shoved the glass through the front of the frame, rather than putting it into the back of the frame. She broke the glass, cut herself, passed out (try catching a fainting customer while holding a sick, screaming toddler). Of course, it was all "my fault". But the first aid classes I took came in handy!
Do I miss DIY? Only a little bit, now and then, with really sweet customers.