Arbitrage

Arbitrage is the oldest business model there is: find the same thing priced differently in two places, buy low, sell high, keep the spread. Retail arbitrage does it with clearance stock and marketplaces. Labour arbitrage does it with wage differences between countries. Information arbitrage does it with knowledge one group has and another wants.

The catch is that arbitrage is self-destroying. Every trade you make narrows the gap you are exploiting, and every competitor who notices narrows it faster. Treat arbitrage profits as funding for something durable, not as a business you will still be running in ten years.

The spread is always thinner than it looks. Forty units bought at $12 on clearance and sold at $29 on a marketplace looks like $17 each, until 15% marketplace fees take $4.35, shipping takes $4, and returns take a couple of units. What is left is about $8.65 a unit, $346 for the batch, before counting the evening spent sourcing it.

Every arbitrage has a half-life, and it is worth estimating before you commit. A specific product on a marketplace lasts weeks once other sellers see the rank. Wage differences between countries lasted decades. The long ones are always protected by something - a licence, a relationship, information that is not online - and the short ones are a way to raise cash, not a business.