The answer to this question is really simple. Just like with any item that is in demand, the purchase price goes up. It's the law of supply and demand. When I have someone come in and request for a preferred writer, the first thing I do is check that writer's work calendar / workload. Then I consider the following:
1. How many papers have been assigned to this writer?
2. How far apart are the deadlines?
3. Are there preferred writer assignments already? If so, how many?
4. If there are only regularly assigned papers, how many of these work orders can I take off his plate to accommodate the requested writer order?
Of the 4 considerations, it is the last one that is of the utmost importance to me as the company owner. I will be reassigning papers to help this writer meet the demand for his services. I need to make sure that my percentage of the final payment will be worth my while, as well as the writers. Hence the additional 20 percent charge for preferred writers.