The California Bar's Ethics Committee recently issued an opinion on whether an attorney negotiating for a client can engage in some forms of “exaggeration, posturing or puffing,” such as overstating the client's “bottom line” settlement number. See Formal Op. 2015-194.
The Committee concluded that exaggeration, posturing and ‘puffing’ are acceptable but that statements that constitute misrepresentations of material fact upon which the opposing party is intended to rely are impermissible.
According to a report in the BNA/ABA Lawyer’s Manual on Professional Conduct, the committee generally embraced the analysis the ABA ethics committee used in its 2006 opinion on the subject, ABA Formal Ethics Op. 06-439. You can read the report here.