[...] small print "fulfilled by McDonalds" [...]
Brilliant! ![Cheesy :D](https://www.eevblog.com/forum/Smileys/default/cheesy.gif)
Some buyers are willing to pay a higher price for the benefits of buying from a high quality vendor. And if that vendor then drops the quality level to that of the cheap competition, they will no longer be willing to pay as much and are more likely to look at alternatives.
But companies like Digikey are relying on the fact that a majority of customers will probably end up paying top dollar for the McDonald's product, without knowing any better... they will hope that the customer experience isn't too terrible overall... and they will hope that people like you or I just check the appropriate box when doing our searches!
Maybe or maybe not. TBH, fulfilling a product at a markup where the vendor is well known for a good return policy, warranty, trust with online payments, physical presence is something done for eons now. IMO that is what the vendors are trying to leverage with the "marketplace" model.
However, this is partially fulfilled by eBay and, more recently, by Aliexpress and Banggood, which changed the game for the western market by reducing the risk to access the McDonald's product. This is particularly true for the transnational transactions.
BTW, brands with local presence operate on this game a lot longer: Greenlee, Voltcraft, Reed, B&K Precision, Commercial Electric, just to name a few in our trade.