I have done several mystery shops with ICU Associates when I was offered a bonus. This company will offer high bonuses (including mileage and tolls) towards the end of the month to complete open shops. I did a shop very close to my house and was paid quite handsomely for not so much effort.
The shop reports are easy to enter and do not require substantial narrative. I receive emails when shops are open and when they are in dire need of you to do a shop you'll get several emails. You can negotiate fees with them towards the end of the month. I found the scheduler I dealt with to be very professional and payment was made via paypal on the timetable expected.
As always, it's FREE to sign up for these companies. You're under no obligation to do any shops whatsoever.
To learn more about mystery shopping, please read my Mystery Shopping 101 post. For a list of other mystery shopping companies I have discussed click here.