The sale price isn’t your profit
A $50 sale is a transaction. It is not automatically $50 earned.
Start with the complete picture
Track customer revenue excluding marketplace-collected sales tax, acquisition cost, selling fees, postage, supplies, and any grading costs. Also account for refunds and shared overhead.
A hypothetical example
Suppose a card costs $15 all-in and sells for $40. If fees and fulfillment total $12, the transaction leaves $13 before shared overhead and tax. The $15 recovered purchase cost is capital you can reuse; it is separate from the $13 margin.
Inventory can hide cash problems
Unsold stock and cards at a grader are not spendable cash. A business can show a profit while still lacking the cash to make an owner withdrawal. Reconcile actual payouts and committed expenses before transferring money to household goals.
Measure your time too
Record time spent sourcing, researching, listing, packing, and handling customer questions. Profit per hour helps you decide whether the work fits alongside school and a job.
Keep tax planning separate
A tax reserve is a budgeting tool, not a tax calculation. Income, withholding, location, and business circumstances affect what is due. See the IRS self-employed tax center for official information.