Tracking profit on flips means recording every cost tied to an item, from the hammer price to the final selling fee, then comparing that total to what the item sold for. Most resellers get this wrong not because the math is hard, but because they forget to log half the costs. This guide walks through the full cost stack, a worked example, and the mistakes that quietly eat your margin.
The full cost stack for a flip
Profit on a flip is the selling price minus everything you spent to get that item into a buyer’s hands. That is more than the price on the auction paddle. A realistic cost stack looks like this:
- Purchase price. The hammer price or the tag price you paid.
- Buyer’s premium. The percentage auction houses add on top of the hammer price. See our guide to buyer’s premium for how this is calculated.
- Taxes and fees. Sales tax, sale fees, or a flat lot fee charged by the venue.
- Repair or cleaning costs. Parts, cleaning supplies, or a technician’s time if you pay for repair work.
- Selling fees and shipping. Marketplace commission, payment processing fees, packaging, and shipping if you ship the item.
If any one of these is missing from your records, your profit number is wrong, usually overstated. The point of logging purchases in an app like LotsRoute is to have a place to put every one of these costs against the item as they happen, instead of trying to remember them later.
A worked example
Say you buy a vintage lamp at an estate auction for 100 units (use your own local currency for all figures below). Here is how the full cost builds up:
- Hammer price: 100
- Buyer’s premium at 18%: 18
- Sales tax on the total: 7
- Cleaning supplies and a new bulb: 5
- Total cost so far: 130
You later sell the lamp online for 220. The marketplace takes a 10% commission (22) and shipping costs you 12. Your selling costs are 34, which brings your total spend to 164. Your profit is 220 minus 164, which is 56, not 220 minus 100, which would have overstated your profit by more than double.
This is why buyer’s premium and selling fees matter so much. On this single lamp, ignoring them would have made a 56 profit look like a 120 profit.
Common mistakes that inflate your numbers
- Forgetting buyer’s premium. This is the single most common error. If your notes only show the hammer price, your cost basis is too low on every item bought at auction.
- Bundling lots without splitting cost. If you buy a box lot of ten items for one price, recording the full price against just one of those items makes that item look unprofitable and the other nine look free.
- Ignoring unsold stock. If you only calculate profit on items you have sold, you can look profitable on paper while a growing pile of unsold inventory quietly drains your cash. Track your unsold count alongside your profit, not instead of it.
- Skipping small expenses. A few units for cleaning supplies or packing tape do not feel worth logging, but across dozens of items a year they add up to a real dent in margin.
Profit per item versus profit overall
It helps to look at profit two ways: per item, and across your whole operation for a given period. Per-item profit tells you which categories or sources are worth your time, for example, if lamps consistently outperform kitchenware once all costs are counted. Overall profit tells you whether the business is actually working, since a few big wins can mask a pile of small losses sitting in unsold stock.
Reviewing both numbers regularly, not just at tax time, helps you catch problems early. If your overall total spent is climbing faster than your total revenue, that is a signal to slow down buying and focus on selling through what you already have.
What to log for every item
At minimum, record the purchase price, buyer’s premium, any repair or cleaning cost, the selling price, and selling fees for each item. LotsRoute is built around exactly this: you log an item once against the event where you bought it, add expenses and buyer’s premium as they come up, and the app shows your total spent, total revenue, and unsold count without you keeping a separate spreadsheet.
Whether you use LotsRoute, a spreadsheet, or a notebook, the habit that matters is logging cost details at the time of purchase, not trying to reconstruct them at tax time or when you finally sell the item months later.
