WTF, black marketers aren't going to pay the tax. How would you do it? 23% on top of the price of the item is a big chunk. Avoiding that tax would be a cottage industry. It assumes that people will willingly pay the tax because it's "fair". Nothing would be further from the truth. You'd get less than expected. Enforcement costs would be astronomical and when you try to raise the tax, today's revolt would look like a love fest.
What kind of items do you expect to be buying in this black market? Groceries? Big screen TVs? You think Best Buy is going to go along with avoiding sales tax, for you?
Maybe not, but they'd lose out to those who do. Also, it would destroy used car dealerships. Who's going to pay 23%, when you can do a private sale? Even today at 5% people make up bills of sale for less than the actual amount, so that when you go to register the car, you don't have to pay as much sales tax. Just think what would happen at 23%, no one would go to a dealer required to report the full amount.