The guy at Delta has to tell you that and it is partly true. The external of the faucets are pretty much exactly alike. The main difference is the internal parts. Don't misunderstand, the internal parts are actually interchangeable for the most part. The main difference is for instance on a Delta 400 single handle kitchen faucet I buy from a box store will have a plastic or nylon ball where the one I purchase from Ihrie or Wilkinson will have a stainless or brass ball. Other faucets will have plastic vs ceramic cartridges. What I would recommend if you don't believe your local plumber is to go to a supplier and actually pick up a Delta faucet and feel it. Then go to the box store and do the same. I think you will feel the difference in the weight. Here is the real reason I recommend buying your faucet from me and I buy it from the supply house; if I buy it and install it I give you a no questions asked warranty for 2 years. If it drips or leaks or any other issue the supplier gives me a new one and I install it and you are happy. On the other hand, if you supply the faucet from a box store I can't do that. It just takes too much time on the phone and in the store for me to warranty it. I warranty the labor only in that case so if it leaks I charge you again because it cost just as much for me to install a faucet that leaks or drips as it does one that doesn't. I've even had customers want me to install a faucet they removed from an old house 5, 10 or 15 years ago and " It worked fine then." I always try my best to talk them out of that because the sales, o rings etc are too old and cracked and I've never had one not to leak. Good luck. Answer from swmpfox on reddit.com