I'm not sure from your post if these are three seperate gigs, or one grand opening for three stores.
The biggest thing you've got to figure out is what the client has in their mind. Many times they have an idea of what they want and are unable to express it...they assume that you are the same as something they once saw somewhere else, so you'll do what they need. Your next conversation with them needs to focus on what EXACTLY they want.
They may not know what they want, which is also common. You may be able to help them pick a plan that will work.
A couple possible examples:
- A platform in an courtyard in front of the new stores. Then you'd be able to set up a small stage show, have scheduled times for the shows, and even include a sound system...which would allow them to give away prizes (coupons for free hot dogs, Radio Shack battery cards, etc.) from the stage. You could MC this for them, too. ("Hey kids...who wants a free battery card?? Well, here's Bob from Radio Shack!!!")
- Strolling. Sometimes people want you to add "atmosphere," which translates into "having a guy wander around and show people tricks" (which you already suspected.) This can work OK if it's in an area that looks like a party is going on, but if you're in a typical small, cramped Radio Shack I don't see how you wander around. You might be able to get a counter away from the cashier, and do small shows there.
Unfortunately, many clients see magicians in the same category as clowns...a cartoony character that does tricks to people.
If the client wants "atmosphere" then they may really want a clown or similar performer. To this kind of client, the costume is perhaps the most important thing...the more outlandish, the better. Unless you have experience performing as a costumed character (just like the guys at a theme park) then you might want to consider passing the gig to a clown.
After all, clowns and Radio Shack go together, right? :D
On the other hand, whenever I've seen costumed characters successfully work at an event (like the 4th of July celebration near me) they're just people who dress up in an appropriate costume and have fun talking to the kids in the crowd. This year the city had two guys on stilts dressed as Uncle Sam. Their costumes were the kind in which the pants legs go over the stilts, so it looks like the person has six-foot long legs. They walked around towering over the crowd, talked to the kids, held out their hands and asked the kids to give them a "high five" and so on. It was fun.