I do have books and t-shirts and bottles on my shopping cart.
USPS has options to box and envelope.
If I'm selling the book of even one t-shirt, it can go on a envelope, but bottles can't.
The problem is that since
"Priority Mail International Flat Rate Envelope "
is way less expensive then
"Priority Mail International Flat Rate Box "
users may check the shipipng method to be the first one when it should be the second.
How do you deal with that?

Thank you