I would emphasize the size of the betta's prospective home: Anything less than a gallon should be avoided, larger sizes are better for the betta to swim around in. Water should have conditioner added prior to adding fish. Water should be changed frequently, even if it appears clear. You could make the point that there is some work involved in keeping a betta, but that the intricacies of doing so are quickly mastered; perhaps frame the matter in terms of a rough estimate of time spent per week tending to each betta. You might want to introduce the idea of having a heater. I resisted getting a heater for a long time, thinking my bettas were "fine," but heaters really make a considerable difference in quality of life. But you might broach this topic (heaters) as an "addendum" to an introductory flier, lest you overwhelm. I notice that PetSmart and PetCo have fliers they distribute--pick one of those up and fill in what they leave out, keeping in mind that a flier needs to be brief and readily available to have impact. Good luck!