A recent buyer chose media mail for an article of vintage clothing in my shop. It's only a couple dollar difference, but it matters with an inexpensive item. How do I go about getting her to pay the additional cost for Ground Advantage or Priority? I'm not sure how to go about it.
You offered the buyer Media Mail. You should just mail it Ground Advantage and take the loss.
I would just cover it. It's up to you to ensure correct shipping options are offered. If you use calculated shipping, just uncheck options you don't want the customer to use. At least when mistakes cost us, we usually only make them once.
firstly, deactivate the media mail option from your shipping profiles, and any other method of shipping you are not interested in offering.
2ndly, I would just ship it since it's only a few bucks on an expensive item as you say.
Would you really want to
A - cancel the order and advise the buyer that you can't ship via media mail, and ask them to repurchase it?
or B - send the buyer an etsy listing link to pay the difference in cost?
You may annoy the buyer with your mistake and lose the sale altogether.
If it is not a book, don't have media as an available option.