What structured data do unique high-value items need?

Each item needs its own record rather than an entry under a shared model: identifier, condition, provenance where publishable, specifications, and price or availability. The distinguishing requirement is that condition and provenance attach to the individual object, not to the product line it belongs to. Per-item records also give each object its own addressable URL, which is what lets a buyer searching a specific reference arrive directly.

Reference and model numbers map to identifier properties such as mpn or productID; serials and certificate numbers map to additional identifiers. Keep each one in its own field rather than concatenating them into a description, because only separated values are matchable — and the buyer who knows exactly what they want is the most qualified traffic in these categories, and the easiest to lose.

A catalogue product is one model with many identical units varying by size or colour. One-of-one inventory inverts nearly all of that, so catalogue-shaped templates applied naively describe the model and discard what makes the object worth its price. Publish provenance at the level the trade already publishes it, and withhold anything that identifies a current owner or a security arrangement.