An independent appraiser will gauge the sophistication of the collection by asking how much the collector spent on stamps, if the material is mounted for easy inspection, and if the owner had any pieces for which expert certificates were obtained. Any file of purchases with receipts or canceled checks can be helpful. A common mistake is that the collector has not shared an honest evaluation with anyone else. Catalog quotation is not market value. Frequently this is most painfully realized when an accumulation of modern U.S. mint sheets sells at a discount from face value.
Condition is the essential factor in stamp value.
The collector who has acquired damaged or defective copies to fill album spaces is kidding himself and his heirs if the collection is valued or insured at full catalog. In making an inventory, list nominal catalog, the discount value to replace with comparable material, and then the deeper discount value which might be realized at a forced sale. Any collector who stays current with auction realizations knows the difference between the prices for superb copies and the discount realizations for average or defective copies. The late Herbert Bloch once observed that if material came in boxes for sale, it went out in boxes. The seller has no duty to do the job of organizing that the owner didn't care spending time to do.