Artikel 17

1. The validity of a transaction entered into between a third party and another person who would be entitled to act as the adult’s representative under the law of the State where the transaction was concluded cannot be contested, and the third party cannot be held liable, on the sole ground that the other person was not entitled to act as the adult’s representative under the law designated by the provisions of this Chapter, unless the third party knew or should have known that such capacity was governed by the latter law.
2. The preceding paragraph applies only if the transaction was entered into between persons present on the territory of the same State.