Handle paper as an artifact
Wash and dry hands or use clean gloves when appropriate. Support brittle folds, avoid pressure-sensitive tape and do not flatten documents aggressively.
Record the document system
Photograph cover, binding, pagination, stamps, signatures, maps, inserts and any envelope or folder that came with the item. Context can be lost when paper is separated for resale.
Reading value
Scarcity, subject, date, completeness, annotations, provenance and visual interest all affect demand. A common manual with a documented owner can be more useful than an anonymous rare-looking page.
Digitization
Use diffuse light, a level camera and a color reference. Store master images in a non-lossy format and create smaller web copies separately.
Marketplace research
Use listings as research leads, not proof of authenticity. Compare construction, markings, condition and provenance.