Here is a real example of how this can work. I used to be signed up with a MS company that had the nicest staff, but most of their shops paid $8 and required me to front $60 or more and wait up to a month for reimbursement and shop payment. Some of their shops required me to eat on my own dime and still give lengthy narratives.
The schedulers frequently called me or emailed me to see if I would do shops. To save us both time, I eventually told them that I appreciated their interest, but mystery shopping was my only source of income. I explained that food and drink did not pay my rent, and I needed to be paid in dollars. I explained that it did not make business sense for me to lose money by doing such $8 shops when I could do shops for other companies and make a decent wage for my time and get reimbursed on my next bi-weekly paycheck. She empathized and asked me what I considered a decent wage, and I told her what it would take for me to do the jobs.
Going forward, I only received email and phone offers that were bonused enough to be worth my while. I never had to ask for a bonus with this company. The bonuses were always realistic and applied before the offer was made.
I had to terminate my employment with this MS company about a year ago due to something beyond my control . We parted ways respectfully and they said they would always love to have me back if I found that I could work for them again.