When the contact us form is viewed as a page, not a dialog:
1. Write message.
2. Click "Send Message".
3. The Send Message button grays out. - Good.
4. It shows: "Your message has been sent". - Good enough.
5. A second or two later the button goes back to normal. - The user can now click it again! And they do. Sometimes 10 times because they are confused.
Suggested fix 1:
- Leave that button gray so that it can not get clicked again.
Suggested fix 2:
- Instead of a banner coming down briefly saying "Your message has been sent", I suggest replacing the form with that message. That would be standard expected behavior for a form.
My earlier thread for background info: Contact us form > message has been sent > contact us form