Hi Rohit,
There is no limit for claiming expenditure against the gross commission received provided the expenditure must be incurred to earn the income i.e. commission and not for any other / personal purpose.
Further, depending upon how much expenditure you are able to deduct with proper documentation, you will be asked to pay tax on the amount after such deduction to the extent such amount increases the TDS already deducted i.e. 91,566/-
Hence, please note that if the tax payable on your net income is more than that, you will not be eligible for refund.
As for the first question, you can apply for the refund by filing income tax return and disclosing your income as well as TDS deducted therein.
@ Suresh: I'm afraid he won't be able to opt for 44AD provision as the same is specifically prohibited for commission income.
Hope this helps. Feel free to follow up.
Ragards