How strictly are exchanges considered?

Hi all! Thanks in advance for the help!

I recently bought a pair of Madewell jeans and they’re quite nice but a little too big. I thought they’d be okay, but after wearing them for just one day I just don’t think I’m going to wear them at this size and would really prefer a size down, especially because this is way more than I usually spend in jeans. I see in their exchange policy that clothes have to be unworn so I’m concerned if I send them in for exchange it’ll be denied. Does anyone know how strict this is? They don’t have any stains or smells or anything I can see, but no longer have tags. Also, if they denythe exchange they must mail them back to me, right?