If you feel it rises to the level of "reckless disregard", then the SLCSP is $0, but in my opinion the repayment limits still apply.

However, in my opinion it does not rise to the level of "reckless disregard".  Here is how the Regulation defines it:

A reckless disregard of the fact occurs if the taxpayer makes little or no effort to determine whether the information provided to the Exchange is accurate under circumstances that demonstrate a substantial deviation from the standard of conduct a reasonable person would observe

In my opinion, because you client submitted their income to their insurance agent, they would have assumed everything was "accurate".