First of all - if that is your investment activity - your taxable income is a capital gain that is the difference between purchase and selling price. Fees to buy or sell are added to the cost of the property.
When we are looking for deductions - these must be actual expenses.
For investment activity - it might be investment interest if you borrow the money,
and other expenses of producing income. You deduct investment expenses (other than interest expenses) as miscellaneous itemized deductions on Schedule A (Form 1040). To be deductible, these expenses must be ordinary and necessary expenses paid or incurred:
--To produce or collect income, or
--To manage property held for producing income.
The expenses must be directly related to the income or income-producing property, and the income must be taxable to you.
The deduction for most income-producing expenses is subject to a 2% limit that also applies to certain other miscellaneous itemized deductions. The amount deductible is limited to the total of these miscellaneous deductions that is more than 2% of your adjusted gross income.
These include fees you pay to a broker, bank, trustee, or similar agent to collect investment income.
You can deduct office expenses, such as rent and clerical help, you incurred in connection with your investments and collecting the taxable income on your investments.
You can deduct rent you pay for a safe deposit box if you use the box to store taxable income-producing stocks, bonds, or other investment-related papers and documents.
So your actual deductions are mainly base on what expenses you actually paid.