Short answer. Only with the principal's consent. The Civil Code bars an agent from buying the property whose administration or sale was entrusted to him, unless the consent of the principal has been given. Without that consent, the agent cannot become the buyer, directly or through someone else.
What the law says
Agents, the property whose administration or sale may have been intrusted to them, unless the consent of the principal has been given
Civil Code, Article 1491 — Persons Who Cannot Buy. Read the full provision →
The conflict the rule prevents
An agent hired to sell property is supposed to get the best deal for his principal — the owner. If the agent could quietly buy the property himself, his interest as buyer (a low price) would collide head-on with his duty as agent (a high price). Article 1491 removes that temptation. It lists among those who cannot acquire by purchase, even at a public or judicial auction, either in person or through the mediation of another, the class of agents, the property whose administration or sale may have been intrusted to them, unless the consent of the principal has been given. The default is a flat prohibition on the agent buying what he was engaged to sell.
Consent of the principal lifts the bar
Unlike some other disqualifications in the same article, the agent's is not absolute. The words unless the consent of the principal has been given provide the way out. If the owner, fully informed, agrees that the agent may buy, the conflict is resolved by the very person the rule protects. The consent must be genuine — the principal knowing that the person on the other side of the deal is his own agent. What the law forbids is the hidden purchase, where the agent buys without disclosing that he is both the seller's representative and the buyer. Disclosure and the owner's approval are what make it permissible.
No buying through a front
The prohibition also blocks the obvious dodge. Because it applies whether the agent acquires in person or through the mediation of another, an agent cannot sidestep it by having a relative, a friend, or a company buy the property and then pass it to him. If the real, beneficial buyer is the agent, the arrangement falls within the ban regardless of whose name is on the deed. The phrase even at a public or judicial auction closes another escape route: the open setting of an auction does not sanitize the conflict, because the agent's inside knowledge and divided loyalty remain.
If you are the owner or the agent
An owner who suspects his agent bought the property behind his back should look at whether informed consent was ever given, since a purchase made without it is legally infirm and open to being set aside. An agent who genuinely wishes to buy should get the principal's clear, informed consent in writing before proceeding, and should not use a nominee to hide his role. Because the validity of the purchase turns on whether real consent existed and how the deal was structured, the specific facts and documents should be reviewed carefully before anyone relies on the sale.