None of these methods is foolproof. And none of them will work for all types of businesses. But try a few on your advertising efforts, and you'll get a sense of how well they're doing and whether the expenditure is giving you a satisfactory return on investment.
5. Spit Runs: Run two different versions of an ad--with different prices, different products and different time applicability--and measure the difference in responses. This will also allow you to learn which appeals work best with your target audience.