California's ethics committee has issued an opinion about taking advantage of the opponent's unilateral mistakes. The opinion can be uploaded below and under that is an article I wrote for BNA on a similar issue, not focusing just on California. On first glance, the California opinion takes a hard-line, or pro-partisan, view. I may have more to say about this later. Here's the opening question and summary.
[edited since posting. i have been reviewing a different, draft opinion from COPRAC and mistakenly referred to this one as a "draft." it's not. thanks to a commenter for pointing out my error.]
Has an attorney engaged in deceitful conduct by not alerting opposing counsel of: (A) an apparent material error made by opposing counsel in contract language; or (B) a material change made by the attorney in contract language?
Where an attorney has engaged in no conduct or activity that induced an apparent material error by opposing counsel, the attorney has no obligation to alert the opposing counsel of the apparent error. However, where the attorney has made a material change in contract language in such a manner that his conduct constitutes deceit, active concealment or fraud, the failure of the attorney to alert opposing counsel of the change would be a violation of his ethical obligations.