I'm a reseller myself and eBay and Amazon and etsy. I'm not sure if it would count as another form of reseller, but something I do quite frequently is buy from one platform to sell on another. For example right now it's book season and a lot of people buy books from where ever they can to resell on Amazon. I've also bought a lot of stuff on Amazon to sell on either ebay or etsy and vice versa. If you are interested in reselling check out my blog I attach quite a few videos about it.