Final answer:
Complex products are those that require consumers to quickly acquire knowledge and do research. These products can involve risk and consumers may have limited information about their qualities, making it challenging for a market to exist.
Step-by-step explanation:
Products that fall into a category where consumers have little experience and need to do research and acquire knowledge quickly are known as complex products. These complex products can involve a certain level of risk as consumers may be less than 100% certain about the qualities of what they are buying or selling. When there is highly imperfect information about the quality of the products, it may be difficult for a market to exist.