I found this method while searching for a new keyboard online for my laptop because one key was broken. New keyboards are quite expensive. So while searching on ebay I found some sellers selling only the keys one by one, not the whole keyboard just keys, at a lower price than the whole keyboard obviously.
One key is sold at around $5/6 for my laptop model. So I happily bought the one I needed.
These people are buying old keyboards, or maybe just get some old broken laptops for a few bucks on fb marketplace, and then sell the keys apart. That's a great business idea I think. Even if you buy new keyboards to do this method, is still profitable.
A keyboard is composed of around 100 keys, which means $500 minimum per keyboard if you sell keys one by one. That's huge compared to if you were selling the whole keyboard (around $50).
Keyboads are not complicated to store for someone who wants to do this from home, and shipping cost for a key is very low. ROI on this one is great.