Your customers don’t come to your store thinking they’re on Amazon, they come to your store because they are intrigued by your advertisement.
Your store is perceived as an alternative to the marketplace, it is up to you to present this alternative in the best way possible.
It is also important to be clear and transparent about details and condition, as well as being accessible for further inquiries.
This way you will be in control of your store and of your client’s expectation because you're setting them to a level that respect’s your store’s situation.
By working on trust, customer experience and perceived value you will be able to extinguish competition, even when its name is Amazon.