The only time to get an exact and accurate inventory count, and valuation, is at the time the business is being transferred.
To do so beforehand, would mean that any merchandise sold after inventory is taken, but before close of escrow - assuming the store remains open and some merchandise is sold before the deal is finalized - would enable the seller to collect the proceeds from any merchandise sales as well as receiving the wholesale value of that merchandise, even though it no longer is part of inventory and cannot be transferred to the buyer.
As an example, if a bottle of scotch whiskey is counted during inventory, and included in that count when inventory value is made part of the escrow, but actually was sold while the escrow was being conducted, the buyer will have paid for it, but won't have it on the shelf to sell when he or she assumes ownership.
Typically, the store is closed for the inventory count to avoid this problem. Alternatively, the store can remain open while escrow is conducted, with the store clerks making careful note regarding the sale of each item, so the inventory count can be adjusted to allow for what was sold.