Kimjef,
The company you work for is different than most, in that you are an employee, rather than an independent contractor.
There are advantages and disadvantages to each type of work relationship, but one reason that you don't see too many people taking about the employee based mystery shopping programs is that employees are forbidden from talking about it on public forums such as this one.
While the pay rate at the employee based program is certainly higher on an hourly basis that most, I find that being selective with the IC jobs that I take allows me to draw a larger average pay rate over time, after adding in the reimbursement, than working as an employee. As a former employee of the company mentioned, I can tell you that I left the company because the reimbursement for food items at the store was minimal and I was only being paid for my time, as well as having no freedom to choose when I worked.
While everyone has grocery needs to a point and can justify the purchases they make at a grocery store, going to get a haircut on a weekly basis or eating out for fine dining nightly doesn't make sense for most shoppers if it's not fully reimbursed.