Does Supermarket Sweep engage a compliance service such as Sullivan?
I don't know what the '90s/'00s version did, but the 2020s version used ABC's in-house standards and practices department.
Speaking of that version and unannounced rules, there were certain expensive products in the store that had a limit of one per customer, and taking more than one would incur a penalty. Home viewers didn't know about the one-per-customer rule
or the penalty until a season two episode in which the team's final total was so low, Leslie had to explain how that had happened. Which prompted a number of online comments to the effect of "I didn't know that was a rule!"
In the current Family Feud, once they get to the Sudden Death face off (if nobody reaches 300 points), what happens if both contestants miss? I've never seen it but I'd imagine they'd probably edit it out of the show rather than going back to the heads of families for the answer.
I've only seen one time when both face-off participants missed and Steve turned to the heads of the families to continue the question, a few years ago. It occurred near the end of a season and my completely baseless guess is that maybe they were starting to run low on sudden death questions.
But yeah, my suspicion (which I cannot prove) is that on the U.S. version as well, sudden death questions that fail at the initial face-off get edited out.