The ledger, and taxes

Write it down

Money in the app records what you paid, what you sold for, and the net, per unit. Do it the day it happens. In three months that ledger tells you which units make money, which sellers waste your time, and whether your ceilings should move. The app learns your real sales and adjusts your ceilings from them; that only works if the ledger is honest.

Profit is income

In the United States, profit from reselling is taxable income whether or not anyone sends you a form. A payment platform (eBay, PayPal, Marketplace payments) issues a 1099-K above the federal reporting threshold, which under 2025 federal law is $20,000 and 200 transactions; several states report at $600. Cash sales do not generate a form; they are still income. Your cost of goods, mileage, supplies and fees are deductible against it if you are running it as a business.

Keep

• A photo of the cash receipt you write at the meet (date, unit, serial, amount, both names): protects you from "stolen" claims too
• Mileage for every meet (a note in the ledger entry is enough)
• Receipts for repairs, cables, cases, cleaning supplies
• Screenshots of the listing you bought from and the one you sold on

Hobby or business

A few flips a year is a hobby; income is still reported but expenses mostly are not deductible. Regular flipping for profit is a business, which means Schedule C, deductions, and possibly a sales-tax permit for resale in your state. When you cross a couple of thousand dollars in profit, spend an hour with an accountant who has seen a reseller before. It pays for itself the first year.

Sales tax

Selling used goods locally may require collecting sales tax in your state once you are a business; a resale certificate lets you buy inventory without paying it. Rules differ by state. This is a question for the accountant, not for a playbook.