I ran an online pro shop a few years back and I had a disclaimer on the 'shoe' page.....
I provided a fitment guide and warned the buyer bears the responsibility for a correct shoe size.
However, each shop owner could decide whether or not they looked after their customer in this space....what's the harm in stocking it and exchanging (unless the shoe size is not a common one, in which case it could sit on the shelf for months afterwards)
but yes, tough one indeed.