I have worked in running retail, so I can sympathise with the retailer who sold them to you but - The salient matter is not whether you have worn them outside, but whether the retailer can tell that you have.
You can clean them up and make them look pretty good. One tell that I used to look for, was whether tiny pieces of grit had got trapped between the lugs.
The retailer should definitely have made sure that the fit was correct before selling you the shoes.
Edited: 28/04/2012 at 21:56