I haven't done the audit for MF, but I've done the simple Mystery Shop. It was a straightforward MS with no reveal. Just go in, wait for someone to approach you, ask a few questions about a new phone, see what they recommend, do they try to close the sale? Get a business card, etc. I believe the one I did had a requirement for a photo outside the store if a certain poster or advertisement was present.
It wasn't a bad shop, I would consider doing it again at a bonus. I was in the market for a new phone, so I figured it would be double duty: I did one at the base rate and then two more in the $20-25 range. The bonuses in my area came up for somewhat last minute shops, so it helped that I'd done one before and was familiar with the scenario when the bonuses appeared.
Shopper in California's Bay Area