I used to work in a Theatre Magic magic shop. I handed it out on multiple occasions and the gimmick was never found. That's only after te wallet was broken in though, I wouldn't do it straight out of the package, which should only take about a week.
That being said, I feel that this is something that should only be done on an offbeat, the wallet should be away and you should be moving on before they ever really have an opportunity to ask to see it.