Re: Flipping guitars
I bought and sold guitars and accessories for a few years online. Problem is, it takes a LOT of time, materials and space to run that kind of business and the returns are slow. You really need a mini-warehouse and some additional help to be able to turn over enough items for one person to make a yearly living (and I'm not talking about a fancy living, either).
It got to the point where I made far more on the parts than I did on whole instruments, which is probably why you now see so many notable eBay sellers who deal solely in used parts. You can buy a used Ibanez RG for $150, sell the neck for $100, the body for $50, the tuners for $30, the bridge for $60, pickups for $30, etc., and make more than trying to turn over the complete guitar. Even if you stick with complete instruments, the margins are small when you're not a dealer, deals can be hard to find and there are always issues arising from shipping damage, buyer remorse, etc. that cut into your profit.
Not saying it can't be done, because I did it successfully, but be prepared to make very little $ per hour for the time you'll be putting in to do it.