Yes, as a self-employed entrepreneur, you may deduct all business expenses related to your eBay/Poshmark sales. This business activity would be reported on Schedule C of your tax return. Any profit would be subject to self-employment taxes. You do not need to create an LLC in order to file as a self-employed business. Your State would determine if you need a business license to operate online.
Inventory, business assets, income, and expenses are reported in the Business section of TurboTax Self-Employed Online. To find this section, search on "schedule c" to jump to the start of that topic.
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