I am not a lawyer, this is not legal advice, etc.

Assuming you mean the Mexican constitution, it's kind of vague:

Article 6 . The expression of ideas shall not be subject to any judicial or administrative investigation, unless it offends good morals, infringes the rights of others, incites to crime, or disturbs the public order.

"Offends good morals" is not defined anywhere, so it's up to interpretation whether that includes fraud. "Infringes the rights of others" is defined in various places, but in similarly vague terms.

Thanks.

The speech itself is protected, but speech can be deemed a tort in a civil proceeding, regardless. Freedom of speech protects opinions and best-effort reporting of facts, not necessarily all speech. Granted, we have to be careful not to exclude too much from protected speech, or we will never have the right again. The canonical example is causing panic with malice of intent, such as yelling fire!, fire!, fire! in a crowded hall, knowing well that there is no fire and with the intent is to cause a trampling hazard.

Fraud usually has to do with commercial statute (in the U.S., the UCC), where misrepresenting goods is grounds for a civil dispute.