I know this might seem obvious to some people, but I thought it could be useful to show the difference between real and fake invites. I recently got both kinds in my email and so I took screenshots of what both look like.
First up is a fake invite. It's pretty obvious that this invite is a phishing scam since they're asking for my Battle.net account name and password.
Now we have a real invite. Notice how there isn't even a link to account management for Battle.net. Also notice how no information is being request and you aren't being instructed to click some link to go to some site. The only links are to the FAQ, beta forums, and for troubleshooting.
Hopefully this has been informational to at least one person