My experience with GFK:
I agreed to do a cell phone provider shop in Park City, UT (where I happen to live) on 1/16/2015 for a fee of $15 plus a bonus of $10.
The location is about a 20 minute drive from my home. I went to the location @ 10:15 am (their recording said that they open at 10:00).
It was in the middle of a snowstorm with the temperature of -7 (Park City is a mountain town where the Winter Olympics were held in 2002, btw). The store was closed and I waited a full 45 minutes until 11:00 and the store was still closed. I then drove home (another 20-ish minutes through heavy snow/ice, etc).
I documented this in my report along with a pic of the "closed" sign (date and time stamped).
Bottom line = I was paid $3 for a closed shop (figuring the driving time + waiting time + reporting time) = about $1.50 per hour.
I complained about the unfairness of the piddling amount of $$$ that was sent and I got back a copy of their policy regarding closed shops.
This is coming from an experienced shopper who consistently gets 9s & 10s from GFK's arbitrary editors.
I later found out (from another of the same cell phone providers in Park City) that the location that I tried to shop consistently has had numerous personnel changes for issues such as "not opening on time and unreliable associates".
And...they expect me to continue to shop for them? I think not.
And...they can't understand why their business is going into the crapper (partly, I surmise, because shoppers just won't provide the quality work that they expect because of their ham-fisted policies".