I'm always envious of those who do appliance flipping - seems like such a great niche since appliances can be so bulky and hard for normal people to move around. As a woman without muscles to speak of (starting to work on that), even with a van/truck and a professional dolly I think it would be a tough job for me.
I did retail arbitrage for a while - I flipped things by buying clearance/marked down items at Walmart and places like TJMaxx and reselling on Amazon. I was flabbergasted that people would pay $50+ for a shower curtain online! Insane.
Did that on the side for a few months, but a) the research gets tedious, b) the record-keeping for tax purposes is annoying (I'm lazy), and most importantly c) it's not an easily-scalable business. There are people who do scale it (by hiring people to do the legwork, etc) but you still have to compete for the Amazon buy box with other resellers, since it's not a product you make.
I wound up researching more about Amazon FBA (Fulfilled By Amazon) and starting a business creating my own products to sell. I know the big thing recently has been importing products from China for cheap and selling that way (wholesaling) but as many people rushing to do this find out, if your product sells, eventually you wind up competing with 20+ sellers of the exact same thing. So my products are household items that feature my own artistic (I use that term loosely) designs, which mean they're not easily copied. I own the buy box and can set my price, instead of competing with other sellers in a race to the bottom.
It's fun, and a business that can be built slowly - been doing it for a year and a half and have four products currently selling on Amazon (should be more, but again, I'm lazy, and also I made mistakes with a couple early products) with plans for several more by the end of the year. Eventually I plan for it to replace my day job.
So it's not quite flipping, but flipping got me started down this road and into entrepreneurship!