Very good question. Notice, this is a systemic problem with a “Fair” (national sales) tax. And, if you bought/sold and lost money, is there still a tax? Well, that is fine state of affairs.
And, if you decide to buy and sell property in cash (ostensibly with no IRS left to police you), how does the tax get administered? The “Fair” tax is anything but...
The fairtax only collects on new retail purchases , used items are excluded.