This is a working manual, not a motivation book. It teaches one skill: buying things that are priced below what they are worth, and selling them for what they are worth. People call it flipping, reselling, or arbitrage. The mechanics are the same everywhere.

Two promises about how it is written.

No hype. You will not find “quit your job in 30 days” in here. Most people who try this quit because their first ten flips made $5 each and they never worked out why. This book is mostly about why.

Nothing you cannot check. The worked examples use listings of the kind that run through FlipGap’s US feed every week, priced with the fees a US seller actually pays. Every button and screen described here exists in FlipGap today. Where something is a rule of thumb rather than a fact, it says so.

Planning figures, not a payout quote. FlipGap uses a conservative business-reseller allowance for selling fees, postage and returns. Your real marketplace charge depends on the venue, category, account type, seller performance, tax and optional promotion; private selling is fee-free in some markets. Open the advanced calculator and replace the defaults with your own costs before you buy. Product and fee details in this edition were reviewed on 14 August 2026.

What you need: a phone, somewhere to store a few boxes, and between $250 and $600 you can afford to have tied up in stock for a few weeks. Less works, it is just slower.

What this book is not: tax advice, legal advice, or a guarantee of income. Rules on selling as a business, on VAT, and on what you may resell differ by country and change often. Chapter 11 tells you which questions to ask; a local accountant answers them.

A flip is one sentence: you buy a thing for less than someone else will pay for it, and the difference is bigger than the cost of doing the deal.

That last part is where nearly everyone goes wrong. Four numbers decide whether a flip is worth doing.

1. What you pay. The listing price, plus whatever it costs to get the item into your hands — the train fare, the fuel, the postage if it is shipped to you.

2. What it really sells for. Not the highest price you saw on a marketplace. What items exactly like it actually sold for, recently. An asking price is a wish. A sold price is a fact.

3. What selling costs. This is the invisible one. A marketplace may take no transaction fee from some private sellers or more than 13% from a business seller, depending on the country, category and account. Postage to the buyer costs money. And some sales come back: the buyer changes their mind, the parcel goes missing, the item arrives with a scratch nobody noticed. Across everything you sell, count on a few percent of your revenue never sticking.

4. How long your money is stuck. $50 profit in four days and $50 profit in four months are not the same business. The first one, repeated, is a living. The second is a cupboard full of stuff.

Put the first three together and you get the only equation you need:

what you keep  =  real sale price
                − marketplace cut
                − postage to the buyer
                − allowance for refunds
                − what you paid
                − what it cost you to collect it

Here is that equation applied to the kind of listing that runs through FlipGap’s US feed most weeks.

Samsung Galaxy S10 Lite, 128 GB, listed at $110. Items like it sell for about $155.

Looks like $45. It is not.

Ten dollars, not forty-five. Still a possible profit — roughly turning $110 into $120 if the comp and cost assumptions hold — but it is a different decision than the one “$45 profit!” invites you to make.

Now the same maths on a cheaper find:

Golden Sun for Game Boy Advance, listed at $36. Copies sell for about $58.

That is 38% below market, which sounds excellent.

Three dollars. For a message thread, a trip, a box, a queue at the post office, and the chance the buyer says it arrived scratched.

This is the single most important idea in the book. Percentage below market tells you nothing on its own. A 38% discount on a cheap item is pocket change. A 25% discount on an expensive one can be a good day. What matters is what lands in your account, and how much of your money and time it took to get there.

The good news: FlipGap does this arithmetic for you on every listing it shows. Chapter 3 shows you where to read it.