If you sell gift cards what taxes are you responsible for?

If you are a self employed taxpayer then you are responsible for all of your own FICA self employment taxes of 15.3% plus any income taxes on your net profit from your business operation at your marginal tax rate.

You will need to report that income, and any related expenses, on Form 1040, Schedule C, Profit or Loss from the Business operation, or you may qualify to use Form 1040, Schedule C-EZ, TO determine your Net Profit from the Business operation. You will also need to use the Form 1040, Schedule SE, Self Employment Tax form to compute and report your social security and Medicare tax on the net profit from the business operation.

For instructions and forms go to the IRS.gov website and use the search box for publication 334 Tax Guide for Small Business a very good place to start with examples