If the admin fees are taken out of your portion of the commission, you can deduct them on your Schedule C.
You can deduct the split you pay to your Broker only if the 1099-MISC you receive at the end of the year includes the full amount of the commission (yours plus the Broker's). This would be highly unusual.
In most cases, the 1099-MISC will reflect only the commission that you actually received. In that case, you can't deduct the Broker's portion. (But you won't be taxed on it, either.)
**Answers are correct to the best of my ability but do not constitute tax or legal advice.
