To be honest I can't see how you are not making money with PPC marketing.

To take a guess, you are spending alot of money bidding on high competition keywords in a saturated niche.

Direct linking DOES work.
Stats show under 10% of directly linking campaigns do work, but if you can find the right one via testing on a small scale it will pay off.

A friend of mine was doing 3k a day profit purely from copied directly linking campaigns even ones in high competition niches.

PPC marketing does pay off, you wont always find that one campaign that is going to make you a million dollars on your first attempt.

Quite often it can be through trial and error.

Good Luck