Welcome to the wild and crazy world of mystery shopping Tracey.
One tip I can give you is, if you are in North Carolina, try to arrive in South Carolina with an almost empty gas tank. Prices in SC are 15-20 cents a gallon cheaper in SC. Likewise, top your tank off before you leave SC. I think Georgia is a bit more expensive than SC, but not as high as NC, so I would offer the same advice.
>>How do I book the shops early enough, that I can safely back out if I don't get the number of shops I need to justify the trip?
I would counsel you to not back out. While it may hurt in the short run, not flaking on jobs has long-term benefits. I had a route fall apart on me last year, 20 shops in a two day period became 5 shops in one, very long day. Earlier this year I got a call from the same scheduler that I did the 5 shops for...I got 15 shops, again a very long day, but there was a very nice bonus added. She remembered that I did what I had committed to do.
Another thing, add to your list of companies you're signed up with. I'm signed up with 200 companies although I actively work for 15-20. Clients will change the companies that do their shops so, while I may not have any shops with "Joe's MSC" this year, it's possible that I will next year.
Lastly, and a piece of shameless self-promotion, subscribe to Mystery Shopper Magazine, www.mysteryshoppermagazine.com. It's free and contains 3-4 articles per issue that can help give you insight into the world of shopping.
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Have PV-500 & willing to travel.
"Answers are easy. It's asking the right questions which is hard." (The Fourth Doctor, The Face of Evil, 1977)
"Somedays you're the pigeon, somedays you're the statue.” J. Andrew Taylor
"I have never met a man so ignorant that I couldn't learn something from him." Galileo Galilei