The majority of the world is doing their shopping through Amazon. By sourcing niche products and selling them through their platform, you can forgo the tedious work of inventory & shipping (it's all managed by Amazon's FBA warehouses). The tough part is finding the right product, a reliable supplier, and having the cash to make bulk purchases. There's also a ton of competition, but if you can find the right niche, the rewards can be huge.

Blogs offer an incredible opportunity for those with expertise (in a niche subject) to make a real living by sharing their skills and ideas. You start by making a website, building a community, and then selling your knowledge (and related products). This website, for instance, generates money while I sleep, but it takes time to rank and the effort required can be massive. It's takes passion, focus, and expertise, because blogging is no get rich quick scheme. It can, however, be profitable in the long run and extremely rewarding. 

Every business has a Facebook and Instagram, but few small biz owners know how effectively market on the platforms. By becoming a digital marketing expert, you can create your own agency to manage social accounts and develop ad campaigns for small businesses. The competition is steep and dealing with Facebook can offer some real headaches, but if you already have a marketing background, this could be the business model for you!