Product & specification
State the product, grade, technical specification and any non-negotiable quality requirement.
"Timber" is not a specification. "KD spruce, C24 structural, 45 x 145 mm, 4.0–5.4 m, planed four sides, moisture 18% ±2" is. The same gap exists in every commodity: HMS 1&2 80:20 is a different cargo from shredded scrap, and Brent-linked light sweet crude is a different cargo from a heavy sour blend.
Name the standard you will be measured against — EN, ASTM, ISO, ISRI, GAFTA, ENplus — and the tolerance you can live with. If a single parameter is non-negotiable (ash content, sulphur, protein, moisture, FSC chain of custody), flag it as a rejection criterion, not a preference.
Where a spec is flexible, say so. A desk that knows which parameters can move will often find a cheaper origin that still meets your end use.