I rarely buy a product without reading the reviews. In the long run, selling bad products is usually not a good way to make money. (Unless the government is s

I rarely buy a product without reading the reviews. In the long run, selling bad products is usually not a good way to make money. (Unless the government is subsidizing your industry, e.g. for-profit colleges.) And competence of advertising usually correlates with product quality. That's why you're less likely to enter your credit card details in a website that looks like it was designed in 1998. Quality ads serve as an honest signal that the company is making enough money to pay for them. If they're making money, that means people are buying the product, and if they're buying the product, it probably isn't terrible.