If you're not making money by doing it, its a hobby. There is nothing wrong with hobbies, but they aren't business. Want to know if you are heading in the right direction? Are you headed towards money positive? That's your answer.
Why does the Craiglist Flipper add value? The Flipper takes away the random luck factor and distributes goods to those who can best utilize them.
Consider an iPad 1 listed for $10 on Craigslist by someone who just wants it gone. Almost anyone would buy just for the heck of it and take it away from the market even if they already have iPad Air and 3 other Android tablets gathering dust at home.
However, if the Flipper buys it and puts it back on the market at say $100, the person buying from the Flipper will actually have to think before making such a purchase.
So a reasonable Flipper adds liquidity and stability to the market. Unreasonable Flipper (one either putting prices too high or too low) does not stay in business for too long.