I have some spare money and would sometimes loan it to strangers in need on the internet. Let's say that I loan $100 and get $150 back after 5 weeks. Only that $50 should count as my income right? And how can I explain that to the IRS, since it's not a very formal loaning process.
In general, let's say that I sell a product/service to someone at a higher price than I bought it, how would my taxes work, given that I am not registered as owning a business?