Plumbing supply houses cater to pros, and when a retail customer comes in, the prices are often different (if the stuff does have prices on it, the pro often gets a decent discount you as a DIY'er won't). HD caters to the DIY'er, and does not have a discount for pros (generally). So, depending on what you're buying, who you are, the price can differ. Also, often, HD and Lowes package things differently from what is at a plumbing supply store, often with different part numbers. When you find something with exactly the same part number, it is probably the same thing. Proprietary part numbers and supplies, who knows how they may differ. You can't go by the product name, only the specific part number. Rumor has it that to get the price, the big box stores have the supplier eliminate some of the QA/QC steps that go into the wholesale market. Since most of the stuff of the assembly line is good (or they'd go out of business), you probably get something good. The stuff sold at the wholesale market would not be accepted by a pro if it was not good, or perfect...a DIY'er may not recognize it isn't perfect, and accept what may have been a reject to the wholesale market.