Every serious sale — whether at auction or through a reputable gallery — should come with a condition report. Most collectors read them looking for obvious problems: cracks, tears, significant restoration. The more instructive reading is subtler than that.
Condition reports are written by conservators, and conservators are precise. The language is intentionally technical and often hedged. "Minor surface abrasion consistent with age" means something different from "scattered losses to the paint layer." Learning to parse that difference is worth the effort.
Pay attention to what is not said as much as what is. A report that describes framing and support condition at length but says nothing about the picture surface itself is an omission worth questioning. Ask specifically about any restoration or overpainting — this should be disclosed, and it materially affects value.
For works on paper, foxing (brown spots from fungal growth), acidity, and fading are the primary concerns. Many of these are stable and easily treated; others are progressive. A conservator's note on whether condition issues are "stable" or "active" is significant.
For paintings, look for references to the craquelure pattern. Natural age cracks that follow the texture of the paint are normal and generally stable. Cracks that cut across paint layers or show lifting edges are a different matter. "Blind cleat" or "relining" in the report for a canvas work indicates prior structural intervention — not necessarily a problem, but worth understanding the reason for.
Ask for UV photographs if you are spending a meaningful sum. Under ultraviolet light, restoration becomes visible as dark patches against the natural fluorescence of aged varnish. This is standard practice at auction and should be available on request through any serious gallery.
None of this is reason to avoid works with condition issues — many extraordinary pieces have histories of conservation. The point is to price that history into your decision accurately.