Buying on the dip isn't always an opportunity. Finding bargains in the stock market is the foundation of value investing. As the theory goes, undervalued stocks will rise to their intrinsic value given enough time. But cheap can mean so many things, and it tends to be quite subjective. Bank stocks, for example, generally trade at much lower valuations than other stocks, and growth companies can boast high price tags, even when they're generating steep losses. Then, there's the question of whether or not a " ...