Short answer. Usually not. The Civil Code treats a mere expression of opinion as something short of fraud, so ordinary sales talk — "best in the market", "you will not find better" — does not by itself void a contract. It becomes fraud when an expert says it and you relied on that expertise.
What the law says
A mere expression of an opinion does not signify fraud, unless made by an expert and the other party has relied on the former's special knowledge.
Civil Code, Article 1341 — Expression of Opinion. Read the full provision →
The law expects buyers to discount sales talk
Every seller praises what he is selling, and the law knows it. Because such statements are understood by everyone as puffery rather than information, they are not treated as the kind of deceit that induces consent. The rule protects commerce: if every enthusiastic adjective could later unravel a sale, no contract would be safe. So a buyer who now regrets a purchase cannot build a case on the seller having called the item "excellent", "top quality" or "a steal". The complaint has to rest on something firmer than the seller's enthusiasm — a statement of fact that was untrue, or a fact deliberately concealed.
Where opinion stops and fact begins
The line that matters is not how strongly something was said but whether it can be checked. "This is the finest car in its class" is opinion. "This car has never been in an accident", "the engine was replaced last year", "this land has no other claimant" are assertions of fact, verifiable as true or false, and a seller who knowingly misstates them is not merely puffing. The same is true of concealment: staying silent about something the seller had a duty to disclose can amount to fraud even where nothing false was ever said out loud.
The expert exception
The article's exception is narrow but real. When the person giving the opinion holds himself out as having special knowledge — a jeweller valuing a stone, a mechanic assessing an engine, a technical specialist appraising equipment — and the other party relied on that knowledge rather than forming his own judgment, the opinion carries the weight of a representation. Two things must be present: expertise on the speaker's side, and actual reliance on the other. A buyer who ran his own inspection, or who had every means to check and chose not to, will find it hard to say he relied on the seller's word.
What is at stake, and what it does not cover
Fraud that induced the contract can be a ground to annul it and to recover damages; fraud on a minor point generally sounds only in damages while the contract stands. This provision governs consent at the moment of contracting. It does not address defects that surface after delivery — those fall under the seller's warranty, which operates independently of anything the seller said. Nor does it displace the disclosure and advertising rules that apply to consumer goods and regulated products, which can bite even where the Civil Code would not. Because so much turns on precisely what was said and what you did before signing, keep the advertisement, chat messages and quotations, and have the facts reviewed before filing anything.