Complex buying behavior is one among various famous buying behavior that consumer exhibits. Complex buying behavior is seen when there is a high involvement and high difference. I know so far the wordings would sound complex, but in fact it is very simple. Think of something that you use very often and that has many significant differences among other similar products available in the market. An example to someone of my age would be buying a car. Think of yourself buying a car, what would you do?? Would you walk straight into a dealer and say “Ah the red one looks nice, I'll have it”. Of course not unless you are a billionaire and money is something you don't really care about. What you actually do is, you take your time and go through a rigorous set of studies. In fact, people go through a complex set of process simply because people perceive things differently. One person might think the first thing to look for would be fuel efficiency and other would say price. Someone else would say it's the speed, or may be looks(i.e how good the car look). Although unconsciously, we go through a very complex set of decision making process which is very hard for even the marketing experts to fathom. This is exactly what a complex buying behavior is. The process is actually termed as “complex buying behavior” because buyers do extensive study about the products, and it is really hard for a marketing expert to understand which buyer would do what. Even among people who buy economic products, someone would look for a car that has least price, some would look for the car that has the best mileage. I hope my answer isn't too complex. -MANISH
Complex buying behaviour means that there are differences between brands and a high involvement.