Hi! I offer first class or Priority Mail options. It is their choice. Clothes don't weigh that much so you can get a lot of them into a first class package without going over the 13 oz. max before you have to ship PM. If they need something super fast, PM is the way to go.
I always purchase the tracking so i can make sure the packages arrived. You can do that through paypal with first class and Priority mail. If you go throught he USPS website, you can only print out PM. It cost a little extra to get the tracking but it is worth it to me to make sure the packages arrive safely. I also send the tracking information to the customer so they have it too. They will know when their package ships that way.