Commentaries on the UNIDROIT Convention 1995

Article 4 lists criteria without ranking them. In practice, judges give particular weight to two elements: consultation of a register of stolen property, and the gap between the price paid and the market value. An abnormally low price is a warning sign that is hard to ignore.

The buyer's status also matters: a professional is expected to carry out more checks than a private individual. Diligence is therefore proportionate to the buyer's status, experience and means.

The three-year period runs from knowledge of the place and the possessor. Case law requires that this knowledge be effective and reasonably identifiable: a mere rumour is not enough, but a precise publication of the work in a catalogue can start the clock.

The absolute fifty-year limit is calculated from the theft. It does not apply to certain categories (monuments, archaeological sites, public collections), for which the State may provide longer periods.

The Convention also has an indirect normative effect: even in non-party States, it serves as a reference for assessing buyers' good faith. Museums and auction houses draw on it in their acquisition policies.

This diffuse influence explains why its importance far exceeds the number of its States parties. It helps establish the idea that a professional buyer must make enquiries before buying.