Build a Marketplace Arbitrage Finder in 50 Lines of JavaScript

Build a Marketplace Arbitrage Finder in 50 Lines of JavaScript I flip stuff on the side. Not full-time — more like "I check prices when I'm bored and occasionally make $50 on a guitar pedal someone underpriced on Reverb." The tedious part was always manually searching the same item across multiple platforms. So I wrote a script that does it for me. It checks TCGPlayer and Reverb, compares prices, and spits out anything with a meaningful price gap. Here's the whole thing. The Idea Price arbitrage = same item listed at different prices on different platforms. A Boss DS-1 pedal for $35 on Reverb might be $55 on eBay. A Charizard card listed at $12 on one platform might sell for $20 on another. The trick is finding those gaps before everyone else does. Setup You need Node.js and a RapidAPI key (free tier works for testing). mkdir arbitrage-finder && cd arbitrage-finder npm init -y npm install node-fetch Create a .env file: RAPIDAPI_KEY = your_key_here The Script Here's find-deals.mjs — the