As a general rule anything you find probably won't scale that well because any arbitrage opportunity which has the potential for scalable returns will generally

As a general rule anything you find probably won't scale that well because any arbitrage opportunity which has the potential for scalable returns will generally be identified and exploited quickly – thereby closing any opportunity which previously existed. Most people I know who have done this successfully either have some niche interest, or do it with something that geographical barriers – both of which make larger profits hard, because you'll be dealing prohibitively small markets. Probably the easiest arbitrage opportunity is furniture. If you live in a city you'll find there's an endless supply of decent furniture that people are trying to get rid of. My girlfriend often collects free furniture that people are giving away and then resells it for $20 - $30 with very little effort. From time to time I'll up-cycle some of it and if you do a good job you can make $100 - $200 profit, which sounds good, but keep in mind it typically takes several hours of work to up-cycle a cabinet so it probably pays less per hour than your day job if you're a software engineer. The other thing I've seen work is buying and selling niche items which have surprising resell value. Musical instruments would be a good example here. You'll find certain items like vintage synths and other retro musical equipment can sell for really good money despite many people believing they're worthless junk. If you know what you're looking for you'll occasionally find great deals locally which you can then resell online. Omnichords are one of those weird instruments that people often give away assuming they're worthless toys but are in fact worth several hundred dollars online.