The general misconception is that all memory is exactly the same, and that as long as the capacities are equal, you should just take the cheapest price. The first thing to realize is that all memory is not created equal, and that it's critical that you purchase modules that are well made, and can deliver the speeds required by high-end imaging systems. The second thing to understand is the value that your memory supplier builds into the product. There are some great memory manufacturers out there, who do the right thing in making memory that works. These are companies that work closely with CPU manufacturers as new machines are being developed, and make sure that all of their modules are built to spec.
Manufacturers also tend to support their products better than a broker or other memory middleman.
They usually offer a lifetime guarantee, and have knowledgeable personnel who can answer specific questions about installation and applications. One thing that I have learned over the years is that it is important to build a relationship with a vendor, and to take advantage of their expertise. Manufacturers may be a little higher in price than a broker who's looking to unload some inventory quickly. In this case however, the extra price is probably worth it, given the development and support that comes with doing business with them. In addition, they are savvy in the memory marketplace, and over the long haul, they may be more competitive.