I do not see how gross receipts could be categorized as "income". Assuming the intermediary - ebay or paypal or other - collects out any sales tax, the gross merchandise payment is still not all income. Income is only the amount in excess of cost for the seller. I know
sales tax is usually calculated as a percentage of sales price, but that and shipping and item price are not all income, that is gross receipts, which is the amount of the money transfer but not the actual net "income". Am I wrong?