I sort of agree with what you are saying, and had the same question. Obviously when looking at vendors, one must take into account the price of their raw materials and the services that they perform. I agree that something like this should be done in the planning phase rather than the executing phase. The way I thought about it was let’s say you found this vendor who you thought fit the requirements of your project and waited until the executing phase to contact them, what if the vendor changed or went out of business. Now you’ve wasted a whole bunch of time for essentially nothing because you’re back to the drawing board on finding a new supplier that fits your requirements. However, what I think the lecture was referring to was maintaining proper risk management of suppliers which is done in the executing phase. One of the departments that plays a huge role in the entire project management cycle is Quality Assurance. They are responsible for dealing with failed vendors and ensuring that the proper preventative actions are taken so the project does not take a big hit.