That's not true. Many merchants simply use Amazon as a storefront and are responsible for their own inventory and shipping.
See this frying pan for instance.
THis is sold by a company called "firefly buys" and it clearly says:
"Dispatched and sold by Firefly Buys in certified Frustration-Free Packaging."
Whereas this one: https://www.amazon.co.uk/gp/product/B004T6PRWM/ref=ox_sc_mini_detail?ie=UTF8&psc=1&smid=A3P5ROKL5A1OLE
clearly says:
"Dispatched and sold by Amazon in certified Frustration-Free Packaging."
You can get vastly different prices on some items (as shown here) but i only trust items fulfilled by Amazon for the most part. Always look at the shipping price as well as yu can see while the firefly buys one is much cheaper, they charge €42 for shipping which brings it to basically the same price.
*edit: sorry, didn't realize you were the OP and were referring to all the items you ordered
I think so too. The pan with the lid is reasonably priced, while the other is very high.
A third party seller has the pan alone (with the same model number) on Amazon US for $105:
https://www.amazon.com/All-Clad-Stainless-Tri-Ply-Dishwasher-Cookware/dp/B004T6PRWM/
Amazon has the pan and lid set for $100:
https://www.amazon.com/All-Clad-Dishwasher-Stainless-Cookware-Silver/dp/B00FUF5OIS/