Sounds like the best practice for our part is to assume that the congrats page is going to give us credit and stop there.

A best practice from their end might be to prevent someone with the same email from taking more than one survey with them per day. This would affect the SM survey where the same person was doing each one, but they could give a window where you could change the person/email for that second survey with them. Not sure how this would work program wise but I'm sure computer smart people could figure out how to make this work.

Since I have someone take surveys for me I've just advised him to make sure he doesn't try to go back and take another (like he has just told me he was doing). I already had one day with 2 surveys credit and don't want to be banned for his honest mistake!