I don't know if vendors have a preference. The key is easier to access when it is not inside the encrypted message, obviously since they don't have to decrypt the message. That saves the vendor time, and they are always complaining about things that waste their time. On the other hand, putting the key inside the message gives you more privacy, since anyone who can access your message can import the key and see the key ID. If your key ID can be linked to your forum account and you're trying to separate your forum and market accounts, then it's better to send your public key in an encrypted message. You don't need to send the vendor your key at all unless you expect them to message you with sensitive info. Some vendors send tracking numbers to their customers. In that case, I'd include a message along with my address that says either don't send me the tracking number or use this key to encrypt it to me, but don't send me the tracking number in plaintext, since that can leak my address. But if you're asking general questions like when the order is going to ship, you don't need and shouldn't expect an encrypted message from the vendor.