Working the sum the other way round
Most resale arithmetic starts from a cost and asks what to charge. At a sale you already know roughly what things sell for and you are choosing what to hand over, so the sum runs backwards: price first, everything that comes off it second, and the purchase price is whatever is left after the target is reserved.
On the figures the page opens with, twelve pieces at $34 with seven of every ten selling means eight sales and $272 of buyer money. The commission, the processing, the packaging and the listing time on all twelve pieces take a large bite of it, and the four pieces that did not sell take a little more on the way to the charity shop. Whatever survives that has to cover both the purchase and the return you wanted on it.
The pieces that never sell are not free
The instinct is to treat an unsold item as a nil — no gain, no loss, it just sits there. It is not a nil. It was cleaned, photographed, measured, described and listed like everything else, and on the default fourteen minutes a piece that is real money at any hourly rate above zero. It also occupies shelf space and eventually costs something to be rid of.
That is why the table at the bottom drops away faster than the sell-through does. Every row buys the same twelve pieces and spends the same listing time on all twelve; only the number of sales changes. Halving the sell-through does not halve the ceiling, it takes considerably more than half, because the fixed side of the lot did not move.
Where the ceiling is most fragile
Three inputs move the answer more than the rest. Sell-through is first, for the reason above. The fixed component of payment processing is second and it bites hardest on cheap items — a flat charge per transaction is a rounding error on a $200 piece and a serious percentage of a $9 one. Your hourly value is third, and setting it to zero is a legitimate thing to do so long as you understand that you have moved the cost rather than removed it.
What the page cannot do is tell you what the sell-through will be. That number comes from your own past hauls, and the first few times you buy a lot you are guessing. Running the calculation at 40 per cent as well as at your hoped-for figure is a cheap way to see how much of the plan depends on the guess.
Related pages
Online store profit takes a single order apart line by line and handles the question of who pays the shipping. The margin calculator is the forward version of this sum — cost in, price out — and settles the margin-against-markup argument. Hourly value is where the rate for your listing time should come from. For a lot you are pulling out of a building rather than buying at a table, salvage value ranks what is worth removing intact.
Questions people ask
What sell-through figure should I use?
Your own, from hauls you have already worked through. Count how many pieces you bought over a period and how many you actually sold, and use that. Until you have that history the number is a guess, and the honest move is to run the page twice — once at the figure you hope for and once well below it — and see how far apart the two ceilings are. On the default lot the gap between 70 per cent and 40 per cent is far wider than most people expect, because the listing time on all twelve pieces is paid either way.
Should I count my own time if I am doing this in the evenings anyway?
That is your call and the field lets you set it to zero. Setting it to zero does not make the time free, it moves the cost off the page and onto you, which is a defensible thing to do while you are learning and a poor thing to do once the hours are the constraint. A useful middle position is to put in a low figure rather than nothing, so the arithmetic still notices when a lot needs forty listings to return the same money as a lot needing four.
Why is the ceiling so much lower than the difference between buy and sell?
Because the difference between buy and sell is gross and the ceiling is what is left after everything else. Commission and processing come off every sale, packaging and any shipping you absorb come off every sale, listing time comes off every piece whether it sells or not, and the return you asked for is reserved before the purchase price is calculated. Take the target return down to zero and the page will show you the plain break-even instead, which is always the higher of the two numbers.
The fixed per-sale processing figure — where do I get it?
Off your own payout statement, the same place as the percentage. It is the flat component charged per transaction rather than per dollar, and the value the form opens with is a placeholder chosen to make the form run. The reason it has its own field rather than being folded into the percentage is that its effect depends entirely on the item price: it is invisible on expensive pieces and can be several per cent of a cheap one, which is why lots of small items behave differently from lots of large ones.
Does this tell me whether to buy the lot?
No. It tells you what the lot would have to cost for your own numbers to work out the way you said you wanted, and nothing more. It does not know whether your price estimate is right, whether the pieces are what they look like, whether any of them can legally be resold, or what else the money and the evenings would have gone into. It also has no view on condition, and a photograph at a sale hides a great deal.