The premise of trade-in arbitrage is this:

At any given moment, there are thousands of items whose selling price as dropped below their trade-in value, allowing you to buy and instantly trade-in to Amazon for a higher amount of trade-in credit, and profit the difference (in credit).

These opportunities aren't super common, but they do happen.

Here's a quick demonstration on how to use Zen Arbitrage to find trade-in opportunity.

Sidenote: Our sister tool ZenTrade is the "lazy man's" way to find these kind of opportunities. See how it works here.