A situation where you cannot quickly find an item during an inspection is not a ground for refusal to admit the entire property. Refusal is applied only if the conditions for import are not met (for example, documents were not provided or a prohibited item was discovered).
Recommendation:
If such a situation arises, inform the customs inspector that the belongings were packed a month ago, the item is located somewhere within this group of boxes, and time is required to open them and conduct a search. Be meticulous when compiling the Inventory of Goods. Compiling this document in detail will allow you to quickly navigate the search for necessary items and will save your time and nerves.