"buying the business is NOT buying an inventory'
Of course not.
The original question raised had to do with disposing of current inventory.
Selling an online business is not that easy as eBay will not allow transfer of a user ID except in case of sale of control of a corporation if user ID was owned by corporation.
List of past customers could be valuable if it is up-to-date and represents real potential buyers for current inventory. Great if the business has a large ratio of repeat customers (like collectors) and basically meaningless if the business is based on "one-time customers" (selling wedding dresses for example!) or the reputation and industry knowledge of the seller. Each case if differenty and will be valued accordingly.
Valuing inventory is always tricky as so many factors are involved. "Cost of Goods" value is OK in many instances but not always.
In some instances, the remaining inventory may have a cost of $1,000 for example but is made of the stuff that did not sell despite much marketing/sales effort to liquidate it. Inventory should be valued at the lesser of "cost" or "market value' (generally determined at the wholesale or liquidation level (how much would a willing buyer pay for it today to buy it all?))