A famous film does not make an expensive poster. A scarce printing of it, on paper nobody has taped, does.
What moves the number
Which printing — original release, later reissue, or modern reproduction.
Size, measured in centimetres rather than named, because formats vary by era and studio.
Paper condition — folds, separation at the fold intersections, tears, pinholes, fading.
What has been done to it — linen backing, repairs, retouching, trimming.
Why two of the same differ
One seller showed the reverse. Everything that has happened to a piece of cinema paper is recorded there and none of it faces the camera. Describing poster condition.
How to find out rather than guess
Establish the printing first, then compare completed sales of the same printing at a similar condition. A reproduction compared against original-printing sales produces a number that will never arrive.
A trimmed sheet is a different object from a full-size one. Measure before you compare.
Reproductions
Perfectly sellable, at reproduction prices, described as reproductions. The value is in the image rather than the object, and the room prices that quickly.
Questions people ask
Are fold lines damage?
Not if the poster was issued folded. Separation at the folds is. Say which.
Does linen backing add or subtract?
It changes what the piece is. Many collectors accept or prefer it on large sheets — undeclared, it is a dispute.
What about lobby cards and stills?
Sets are worth more complete. Say the count, and say whether a set is partial.