Jim...the tax liabilities on $138,000 depend on many factors all of which are up to the discretion, record-keeping, honesty, etc of the seller.
For example, let's say you had bought all of your merchandise under a corporate heading as "office decor" and had added them to your depreciation schedule for your taxes. Let's say, you depreciated them out fully over, 5 years or so, and then you consigned them to an auction. By law, whatever you received from this sale, would be considered RECAPTURING of the depreciation and would be subject to capital gains. That is of course, if you report the income on your tax return. Which, if you were receiving anything over $10,000, once you took the money to the bank in any form (check, cash, m.o.,etc) they would fill out what's called a large-currency movement report that would go straight to the IRS.
If the items you are selling are considered an "estate" then I know the rules are different. Generally, guys have the amount they paid for an item noted + related expenses, so after it sells, there's an established profit-figure which they will pay regular income tax on, providing they report it on their Tax Return. I'm not real sure what you are driving at, but when I have an auction, the income is noted in my taxes along with the dispersements back to the consignors, so one way or another, it's being reported.