Who knows, I've never understood how to profit from flipping.

Look at TP indexing sites often to see if anything is flippable.

Maybe I'm just bad at it but I could never make more than a couple g with it, seems pretty inefficienct if you look at the amount of time you put in vs the ROI.

Whenever I've needed a big chunk of cash, I make a legendary and sell it. That won't work for everyone but at least at the rate I go through money it sets me up for a long time and makes the effort worth it. Another option for slow and steady progress is flax farming. Park a bunch of alt characters at the circle in Mount Maelstrom with reaper's sickles and then sell vials of linseed oil. For the effort and time it's a good return.

The fastest way to make gold will always be buying gems and converting to gold with real money.

Realistically you can break it down like a job. How much would you pay yourself to play per hour? How much gold do you want and many gems/real currency does it cost? Now figure out how many hours it would take to make that much gold.

I watched one of Lara's videos recently and legendary fishing is one of the fastest ways to make gold, but it's also rather boring.