When listing an item in two categories, the primary category determines which condition values can be used. On the eBay marketplace, you may see items that appear to have an item condition specified in Item.ConditionID even though GetCategoryFeatures may indicate that condition is disabled for the category. This can occur when the seller lists in two categories, because the primary category's rules take precedence.

So, for example, on the eBay US marketplace, the Technology Books & Resources (3516) category supports Item.ConditionID, but the Vintage Computing (11189) category does not. So, as long as a listing uses 3516 as the primary category ID and 11189 as the secondary category ID, the listing can use any of the Item.ConditionID values that category 3516 supports.