Check the part number, not the name of the product. If the number is identical then they're the same. If the part number varies by even one digit or letter, then it's a slightly different part made for Home Depot.

You might want to ask this in the Plumbing forum. You'll probably get better answers than in Appliances.

Here is a link that might be useful: Gardenweb plumbing forum

Your best bet with him is to buy the product you can get a better price on without his ok. Tell him you will be supplying those things and they are already purchased. It's not his concern how much they cost you.

some manufacturers do in fact supply slightly different models to the big box stores. Check the model number very closely and compare with the model sold elsewhere. But what is a very common practice is for only the cheaper models to be stocked in the big box stores like Lowes and Home depot. They will order non stocked models for you however. You will usually not get a very competitive price on a special order item however. I got a Toto toilet delivered free shipping using Amazon Prime in two days. . My local store quoted me a higher price and 1 week delivery time.

Another thing that happens more often than you might realize is that the big box stores take on models about to be discontinued or that have been poor sellers for the manufacturer because of what proved to be an unpopular design, or some minor defect or problem and use them for promotional sales. I saw this recently in an American Standard "cadet" toilet promoted by Home depot at an unusually low price. It turn out that every toilet had glaze defects that would not effect use but nevertheless would not have passed cosmetic inspection. These were all seconds, but nowhere was the customer informed! You had to discover this on your own. Buyer beware.

Yes, some mfgs do have parts specific to Lowes and HD. I was looking at ShopVacs made for Lowes just yesterday, and last week bought an HD-specific Kohler kitchen faucet from HD for a laundry reno -- a little more plastic, maybe, and less flash. My contractor was fine with it, but we will see what the plumber says at install. Interestingly, my HD told me they do not sell any Toto products, so I ordered my sink and loo from Amazon. Best price, free shipping, and delivery directly to my garage 48 hours later. Might be a regional restriction?

It's EXTREMELY common for a large customer to have their own SKU in a manufacturer's database for convenience. One look at how many 123456QWERT-1 have shipped tells them how many units went to that customer, regardless of where they were shipped.

It DOES NOT invariably mean that the product is different - changing production line parameters is expensive!

My SO's electronics company made chips for various auto makers ... each major manufacturer had its own inventory number. The difference happened when the chips went through the labeling machines, not in the production line. A giant bin of chips turned into Ford, Toyota, Subaru and BMW parts.

It is different. They do make different lines for the big box stores in many products. For example, Pella windows are also sold in the big box store but they are a very different, lesser quality window, than Pella distributors sell directly. Same would hold true for a toilet. It's a known fact in the industry.

Your contractor is correct as far as olumbing goes. Moen and all the other higher quality name brands out there will change the guts of the plumbing to a cheaper material like plastic to get the price down to what the big name stores woukd like it to be. That’s a fact so be careful.