I have to assume you sold an item of some sort (e.g., from inventory). In that event:
Gross Revenue/Sales: $3,000
LESS cost of item: $2,500
EQUALS Gross Profit/Income: $500
LESS eBay fees (expense): $300
EQUALS Net Profit: $200
Refer to Schedule C (link below) if you are in business.
https://www.irs.gov/pub/irs-pdf/f1040sc.pdf
