Yes, you can deduct the fees as expenses on your Self-Employed Income.
1. Go to the Income and Expenses section of your Business
2. Under Expenses, you can choose whichever category seems to make sense for "Transaction Fees"
- Advertising or
- Commissions or
- Other Miscellaneous Expenses or
Putting these expenses in one of these areas will depend on your consideration and will be acceptable to the IRS
Of course you will have these fees documented for each sale and your records.
https://www.irs.gov/publications/p535#en_US_2016_publink1000208632