Dan, the model is patterned after the parable of the Arab loading his camel. After finishing the day's labor, he noticed a single straw on the ground and immediately flipped it onto the animal's back; he/she collapsed. Thus, the adage of the straw that broke the camel's back was born.
In my 22+ yrs. shopping, in many cases, fees have decreased while inflation and work have been on the rise. An MSC then continues to pay less and less until work can no longer be assigned . Below is a classic example:
In 2007, I was paid $15+$5 to monitor college students appearing for work. That spring, I was paid en extra $5 IF I chose to snap an exterior pic. IF, as in it was optional. Today, I see shops requiring a dozen pics and paying zero for that compliance. In addition, any pic has the potential to render the job rejected.
From a business standpoint, I agree no company should pay an IC more than necessary for work. As contractors, shoppers are free to reject work where conditions do not meet their approval.