I just would not want to discourage someone who might surprise even themselves and make a go of it.. they may just need the bit of encouragement to get them rolling.
I figure if they quit, then all I've wasted is my time, but they've gained knowledge. They then know it's out there, know the basics and how it works, and can return to it if needed.
For example, I've couponed for years, but when that Extreme Couponing show came out, people came out of the woodwork asking me to show them how. On average, I spent about two weeks, sometimes as much as two months, going back and forth via email and phone calls at length, teaching them everything there was to know about it. Out of the 10-15 people I've taken that level of time to teach, only one has stuck with it. But the others, at least they know it's out there, how to do it, and can return to it later if needed.
Knowledge is the most important currency we have to enrich others' lives, and the best part is that it can be had/given for free. I don't consider any of it wasted time.
Honestly, I would encourage everyone to do something other than mystery shopping. I feel like, even if it is a big piece of someone's financial pie, it shouldn't be the whole pie. That's just my personal financial outlook, though, and I know others view it differently.
------------------------------------------------
Plan the work. Work the plan.