He's being honest. The DIY store version often contains less quality internal parts (plastic versus metal) than the version sold through stores like Fergusons where contractors tend to buy.

Yes, but there's a middle ground -- consumers can buy at places like Ferguson's too. The question is are you getting at least as good a price from him (including his markup) as you would be getting if you went to the same place.

I have heard the Home Depot, etc thing frequently. But I have never heard that the plumbing supply stores sell different quality to contractors. I have always understood that it's the source that matters, not the purchaser.

My experience is contractor grade is the bottom of the barrel. I doubt they have different versions of the same model for contractors and ordinary citizens. The company could get in a lot of trouble doing that. More likely some specialty stores offer better models that Home Depot doesn't offer. Or at least they don't stock in the store. I've found that HD and Lowes stock the lower end stuff because that's what sells in bulk. You can go to their website and buy their higher end stuff and they'll usually ship it to the store for free. Plus Home Depot and Lowes will typically give a discount to contractors. Around 5%. If you buy a lot of stuff at once, they'll give them up to 10%.

We bought our Kohler simplice faucet through Home Depot. I got worried when hearing that the Koehler at HD was of lesser quality. I contacted Kohler about this and spoke with a customer service rep who assured me that they were the Kohler products were the same regardless of where they were sold. The rep did say that sometimes a product sold at HD might contain an additional fitting, of a type that a homeowner wouldn't be likely to have but a plumber would, but that the products themselves (in my case, the Simplice faucet) was the same whether you bought it at Home Depot or a bathroom showroom.

Note that something you might get if you buy fixtures through your contractor is an additional warranty if somethings goes wrong (or, at a minimum, the contractor will be the one to deal with tracking down the substitution.)

We did a combination -- ordered the toilet, sink (kitchen and bathroom), faucets, and a number of the external light fixtures ourselves. We had the contractor take care of the tub (because we didn't want to figure out how to transport it back to a store if there was a problem.) We were planning to order the under cabinet lights for the kitchen ourselves but the electrician ended up ordering them for us. A good thing too, because one was broken right from the start.
Our contractor would have charged a 15% upcharge for supplying fixtures (on top of whatever upcharge his sub was charging him) so for us, it was worth it to buy certain things ourselves. For the most part, we used Amazon or Home Depot (HD for things we thought we might want to return if we didn't like the way they looked.)

Thanks for all the various responses. This is a difficult one. I am going to wait to see what types of prices he is quoting then go from there. He seems to be reputable and has a lot of good online reviews.
We shall see.....

Home Depot thing is sometimes true, Answer is the somewhat useless "it depends"

The real problem is that Home Depot is a pain and often charges higher prices. This doesn't apply to online, but there are other real pains involved - a surprising amount of stuff has defects out of the box, and online support/returns is usually more than most want to deal with. I buy stuff for myself online. But would hesitate to install online into someone else's house.

Thanks again for all the responses. Here's the followup:
He finally came back with the estimate, and the prices were considerably higher than the fixture prices I saw online. ( Like by 100.00 for the faucet ).
I am thinking of sending him an email with the links pointing to the items and ask him why there are such huge differences in his prices vs online.
Do you think this is appropriate, or should I just say 'thanks', and move on without being confrontational?
Personally I don't think the outcome would be that he'd LOWER his prices, so I don't know what good my email will do.

I ordered all my plumbing fixtures through my KD, although I guess now she's my BD. Her only fees are she gets a cut of what I buy through her. All the things I bought through her for my bathroom are equal to or less than prices I see at faucetdirect.

Consider this a warning. This is a contractor who Always Knows Best, you know nothing, and he will have an attitude all the way.

BTDT

Personally, I think your contractor just tries to make a profit on all fixtures. I've seen this a lot while interviewing contractors for my master bath remodeling. When I asked questions what is exactly better in the fixtures they offer, I never had a clear answer. I also called Kohler and Delta and asked them if this is true that contractors can get better versions of the products I selected. The answer was no. If the model number is the same, you will get the exact same product.
I would tell him politely but firmly that you will buy fixtures yourself since the online price is much better.

Contractors can get better prices, but from what I understand they usually they pass on a portion of the savings and the other portion is their fee.

If the contractor has experience to know which products are more reliable and have readily available replacement parts, etc. It even seems fair to charge a fair percentage or fee if they provide the product, simply because they are being paid for their expertise. However, it does seem odd that the fixtures are significantly more expensive if they are exactly the same, especially if he purchased them at a lower price.

I would go ahead with e-mailing him, I think you can do it in a way that is curious and information seeking instead of confrontational - include the links showing the model numbers are the same and ask to know what the difference between the products are and what the benefit would be of choosing the more expensive ones - you can always privately verify his response with the manufacturer if you want to. How he handles it will say a lot about what you might do next. Maybe there is a misunderstanding and he is really purchasing a different, higher quality product that looks the same. Or maybe you'll find he is really charging a $100 service fee and opt to order them yourself. Maybe you'll learn just in time he's a shady contractor :)

$100 service fee on hundreds of dollars in fixtures might be reasonable to know they're reliable fixtures and they're covered in the contractor's warranty, but if he won't itemize it for you so you know exactly what you are paying for I would be suspicious.

In my opinion, part of his job is to explain so you as a homeowner are educated about the work that is being done on your property. As long as you don't accuse him of ripping you off before you have enough information, a good contractor will address your concerns and respond professionally.