"plumber grade" vs "big box" plumbing supplies... fact or fiction?

I believe there may be some fact to this. All depends on the product being purchased. The one big difference is this: if you buy it yourself and pay a plumber to install it, any defects will cost you plumbers wages to fix it. If you buy the product from the installing plumbing company, and there happens to be a problem with it, it will be fixed at absolutely no charge. When you buy through the installer, the installer will stand behind the product. When you buy at box stores, or online, the installer has no reason to stand behind it. Always best to get your materials through the installing company in my opinion. Many times we won't even take on jobs when the would be costumer already has all the materials. Believe it or not, professional plumbing companies actually depend on the small profit made by selling plumbing materials, faucets, toilets, showers, sink, etc, etc. And for many of us, it just isn't worth going out and taking a chance on somebody else's materials.

Thanks for the input and I do understand your point about the installer standing behind the products that they sell you. However, the price differences that I'm finding are hardly "small". I randomly compared 3 sink faucets of the same model number between my plumber's showroom and an online retailer. Basically, there's a 25-30% difference. We're going to have our kitchen and 4 full baths to outfit with fixtures and plumbing products. I have no problem thinking I could blow through $12-15,000 without even trying. That equates to $3-4,000 that I could save online, MINIMUM. I would expect the manufacturers to step up if their product malfunctions/breaks and I would have to pay labor for any issues that arise. I could have quite a few issues on our new build before I got up to 3-4K...