There is no 'used good problem'. Used goods simply aren't taxed.
Collection and enforcement are far easier than under an income tax, by far.
The only ones reporting and sending in tax money are those who make retail sales.
And that, as anyone who has been in the retail trade will tell you, is about as easy as any form of taxation can be: Figure your total sales, compute what you owe, and remit the funds.
Most of the states, about 46 I think, already have a simple, efficient and noninvasive sales tax collection system in place.
Those who can't see how much more prosperity and freedom we will have under this system are either blind, stupid or misled.
Or profiting from the current system. Other than that, you are right.
Which, as the article cogently points out, becomes a massive incentive to reclassify items as "used". For example, is a rent-to-own contract a new or used purchase? I know what I'd do: rent a car for a month, return it, and then offer to buy it. Likewise for furniture, consumer electronics, etc. Video stores will clean up by stopping to sell new videos, and instead rent every video out once before selling it used.