Short of giving away someone a light, it's always an uphill battle to convince someone they need to upgrade their lighting when they think what they have can work. The longer they have been in the hobby of fish keeping, the harder it is as T12's were impressive when they started to become widely used. I was not in this hobby but I do remember how excited my dad was to put florescent lighting in our home.
That said, just about the only think I can convince someone who really thinks their T12/T8 lighting will cut it is CLF bulbs. Even though sometimes you can find as good or better of a light fixture new, and often used, it's kind of the same mentality. Everyone always thinks "I know those are very efficient so that makes sense". Even my father, who is all about efficiency and built his house around that (I mean that quite literally, he designed and basically built his house himself with a few helpers with the main goal of being efficient) always thought my T5HO's were wasteful compared to my tanks with CFL's. Now that his ballasts are going out, he's redoing all the lighting in his house with T5HO's, and explaining to me how much more efficient they are.
Not to go on a personal rant here, I just find it to be hilarious how people can be so set in their ways about things they don't know about, my father (and myself included) but CLF's seem to be that place where the cheap skate, the know it all, in the person who is just scared to change can all seem to come together.
If it's not a super deep tank, you can get away with about 1 bulb for ever 1.5 feet or so. Just increase the wattage if you need more light. Plus it's DIY so people instantly assume it saves a lot of money. I mean it is cheap but fixtures can be had for incredibility cheap now a days.