What a Power of Attorney actually authorises: Thailand's agency law behind every POA-signed deal

Overseas buyers on Phangan routinely grant a Power of Attorney to a Thai lawyer or facilitator to sign a sale-and-purchase agreement, incorporate a company, or register a transfer at the Land Office without flying in. The POA document itself only proves that authority was granted and, until Thailand's 2027 accession to the Apostille Convention takes effect, that it was properly notarised and consular-legalised — see the Power of Attorney legalisation guide for that procedural layer. Whether you're actually bound by what the agent then does is a separate question, governed by the Civil and Commercial Code's general law of agency, Sections 797–844.

The core rule: bound only within the scope actually granted

• Section 797 defines agency itself: a contract whereby the agent has authority to act for the principal, and agrees to do so.
• Section 820 — the principal is bound to third persons only by acts the agent performed within the scope of the authority the agency actually granted.
• Section 823 — if an agent acts without authority, or beyond the scope given, that act does not bind the principal unless the principal ratifies it. If the principal doesn't ratify, the agent becomes personally liable to the third party instead — unless that party knew the agent lacked or exceeded authority.

In practice this cuts both ways. A POA drafted with broad, open-ended language ("manage all my affairs in Thailand") can let an agent bind you to things you never specifically intended. A POA drafted narrowly protects you from that, but means anything outside its exact wording needs either a fresh instrument or your own written ratification after the fact — a phone call authorising something extra isn't a substitute for either.

Money and property passing through an agent's hands

Section 810 requires the agent to hand over to the principal all money and other property received in connection with the agency. This matters whenever a lawyer or facilitator temporarily holds a buyer's deposit, sale proceeds, or a refund on its way to Land Office registration or an FET-form-documented transfer (see bringing money into Thailand) — you're entitled to a full accounting of every baht and document that passes through, not just a summary at the end.

The overseas-principal rule that catches people off guard (Section 824)

Section 824 sets a default rule specific to agents acting for a foreign-domiciled principal: an agent who makes a contract on behalf of a principal who is, and has their domicile, in a foreign country is personally liable on that contract even though the principal has been disclosed — unless the contract's own terms are inconsistent with that liability. Concretely, if a Thai lawyer signs a sale-and-purchase agreement, lease, or company document naming you as the (disclosed) overseas principal, the statutory default makes the lawyer personally answerable on that contract too, not just you — unless the contract is drafted to say otherwise. This can work in a foreign buyer's favour (a local party genuinely on the hook alongside you), but it also means the wording of the underlying contract, not the POA, decides who actually carries the liability.

Practical checklist for a Phangan buyer using a POA

• Scope it narrowly and specifically. Name the exact acts authorised — sign the sale-and-purchase agreement for a named title deed, register the transfer at a named Land Office — rather than open-ended authority to "manage all matters."
• Require an accounting. Section 810 entitles you to demand every baht and document your agent received on your behalf; ask for bank statements and receipts tied specifically to the transaction, not just a verbal summary.
• Get ratification in writing if the agent needs to act beyond the POA's wording. Widen the instrument or sign a written ratification afterward — don't leave it to an informal approval that a counterparty or court can't verify.
• Check how contracts are worded when you're the disclosed overseas principal. Under Section 824's default rule, the person signing on your behalf can end up personally liable on the contract too unless it states otherwise — ask your lawyer's contract templates address this explicitly.
• Remember legalisation and authority are two different questions. A POA's notarisation or (from 2027) apostille proves the document itself is genuine — it says nothing about whether a specific act your agent performed was actually within the scope that document grants.

A Power of Attorney only ever authorises what its own wording covers. Before signing one for a Phangan purchase, the two questions worth asking are what exactly you're authorising (Sections 797, 820, 823) and who is left holding a contract's liability if it's later disputed (Sections 810, 824) — the same care you'd bring to vetting your lawyer's fees or working through a due-diligence checklist is worth bringing to the instrument that lets someone else act for you.