The fair commission rate is what someone else would be willing to accept to provide the same service you do. Market value is a reality in comp plans. They might be packaged a little differently, but there is a pretty similar total compensation plan in most industries.
To answer your question, it depends a lot on how much they pay you in salary. If you're salary is reasonable, anywhere between 5-15% of the net. This has a lot to do with how important you are to the sales process. For example, if the company spends a lot on marketing, or is a brand that sells itself, you are typically going to get a little less in my experience.
I don't know what you sell, but if I were working with 14-20K in weekly sales I would want at least 10% and a reasonable salary.
Hope this helps!
Justyn