A good way of making gold is buying low and selling high. I bought a mace other day for 10k for myself but I could've easily got 80k for it. There's lots of bargains like this.
Thieving, questing, farming materials, selling some stuff on the guild trader. I find that if I do too much of one thing I get super bored even if it is good for making gold/collecting motif pages.
Don't think of it like nosy neighbors. For one thing, addons like MM make that sale available for everyone in guild to see. Its not nosy when everyone using MM selling or buying those items in the gui