I picked my user name when I first joined PPRuNe as I was a mystery shopper at the time. It was a perfect job for me while I was completing my modular training during the last downturn after 911. Mostly I did financial product (mortgages, loans and associated insurance) mystery shopping which was a bit more challenging than ordering a Big Mac and fries and timing how quick the queue was!
I had to go into branches of banks and building societies, show interest in a certain product and describe a predefined financial situation and have an customer interview with a financial advisor(FA). I was assessing customer service skills of any staff member I encountered, the FA's ability to recommend a suitable product as well as ensuring compliance with the financial ombudsman guidelines at the time. It was hard work but fascinating and entirely on my own time schedule so it fitted in with the studying well. I didn't get paid (around 30 pounds per interview) if they cottoned on to what I was doing which made it challenging. The company I worked for used to give me a list of branches in my county for me to work through so with some planning I could get through 3 or 4 a day. Sadly they have ceased trading now but I am sure there are others out there.
Cheers.