With the seller in question here, if I wanted a garment (where I was unsure of the brand measurements), I would ask for them.

For the seller to have an enquiry as to fit, and say only that an exchange is ok but shipping would be my responsibility both ways...I would not buy.

Not because the seller is in the wrong. If an item doesn't fit and I return it I expect it to be at my cost, if the measurements weren't specified. No seller mistakes, my responsibility.

But, the seller received an enquiry about fit and could just have sent the measurements right then.

Only saying a return is ok, with shipping at buyer expense, would leave me not buying. As I would have no real idea if I might have to do that. Why risk a loss for the sake of not getting a clear, upfront set of measurements? No thank you.

Always best to know the measurements and no harm in asking. If the seller can't be bothered at that point, no sale.

So as Lurker said, should she really have to? (Ask)

At that point the seller should have provided them.