Accidentally ordered XS when I wanted 4XL. Didn't double-check what size i was ordering bc I was ordering more bras (since I liked the couple I ordered to try em out so much). The return was easy, I just printed out the provided label and re-used the envelope they came in, and in just a little while the ones I actually wanted arrived. So yay!
I'm marking runs small on these, but by that I mean I usually wear what ither brands call a 2XL but here I need a 4XL. No prob, those kind of clothes labels are arbitrary anyway. But the size chart is right, follow the size chart with your measurements and you will be okay.)