Do I have to let the buyer try on the dress?
It's completely up to you to offer a try on.
If a buyer is willing to travel, we recommended letting them try on the dress, as it betters your chance of a sale.
Of course, only as long as you feel comfortable, ie: having a partner or friend with you. If you don't feel comfortable meeting a buyer in person, just explain this when contacted (or include it in your listing).
If you do decide to offer a try on, remember to ask the seller to refrain from wearing perfume or fake tan to keep the dress looking fresh.