I think a lot of people fail when they specifically focus on only a small selection of high-competition keywords. I have gained dominance in a couple of niches thanks to the use of long-tail terms, and without any linking or even trying too hard. The problem comes when making sales from that content, and whether there is enough of a market share to get you a sustainable income.

You might sell blue widgets, but so do three corporations who already dominate. Some people stick to desperately trying to rank against those corporations, when they would be better creating content for "blue widgets with flanges" or "dark blue widgets in America". Then it's simply a matter of having enough pages and items to sell.

For instance, I have no chance of ranking in position one for Fleshlights, the competition is insane and already completely dominated by other larger companies with massive advertising budgets. But, Fleshjack is a smaller market, and I can target long-tail keywords in the whole product range gaining a higher position for those looking for a specific item rather than a range.

Backing up a product page with considerable pages of reviews and other information can also boost the position of the product against competitors.