The Marshalls example is not valid. Sorry.
Grandmaster only quoted part of my original post; in the sentence before “In addition…”, I noted that Marshalls sells closeouts.
However, it bears (pardon the pun) further explanation. If a particular item is widely available at a closeout price, and a store carries it at full price, it might still be ona’ah, despite the fact that the owner might be taking a loss. However, going to a regular shoe store, where you’re likely to find what you need, is a different shopping experience than going to Marshalls, which is more “hit and miss”. A store owner, I think, has a right to charge more for a particular item if he provides a better selection; it’s the same idea as better service.
This from Money – The Bottom Line (Rabbi Kaufman):
Market price for the identical object will vary from store to
store due to such factors as service, store ambiance, and
knowledgeable sales staff [50].
50. Pischei Choshen 4:10:(11 ).