Who built this
I'm Sam. I worked in institutional finance for 15 years at top-tier institutions. Decided to take a career break. During that time, I wanted a side project, something different, so I looked into selling products on Amazon.
Being an analytical person, I did what I always do. I tried to figure out the economics before committing any money. What would it actually cost me to sell a product?
I couldn't believe what I found.
The fees were scattered across dozens of pages. The fulfilment costs depended on size tiers and weight bands I'd never heard of. Shipping costs? Quoted — not published. Payment processing? Buried in the small print. I asked AI. "Roughly $3.50." Roughly? I looked on Reddit. Estimates. Facebook groups. Guesswork. The platforms themselves? Partial answers. Different pages. Different formats.
Every answer I found was roughly. Approximately. An estimate. A range.
I've spent my career in a world where you don't make decisions based on "roughly." You source the number. You verify it. You trace it back. You model the connections. And then, only then, you decide.
So how on earth is anyone starting or running an e-commerce business without knowing what their actual economics are?
I stopped trying to sell on Amazon. Instead, I built the tool I wished existed.
I thought it would take a few weeks. It took over a year. Not because the maths is hard — because the data is scattered across 1,236 published pages in different formats, different languages, different update cycles. No single page tells you the full cost. No two platforms structure their fees the same way. The assembly is the product.
Every fee published by Amazon, eBay, Walmart, and Shopify — extracted, structured, and sourced. Every number traceable to the page it came from. Every connection between costs mapped so you can see what's hidden, what's changing, and what you can do about it.
That's FineMargins.
Sam is a CFA® charterholder. CFA® and Chartered Financial Analyst® are registered trademarks owned by CFA Institute.