One easy way to evade the tax is to make the purchase under the auspices of a business. Since almost everything could be a business expense, plane ticket, meal, hotel room, car payment, gasoline, auto repair, office supplies, etc this is a major loophole.
Another easy way is for people to do services for cash or trade services with each other.
Another way is for retailers of items to simply not report the tax collected and hide the sale. Or to say the item is used, and not charge the tax.
For a 30-50% tax the desire to cheat will be huge and require an intrusive enforcement agency.
"Show me just what Mohammed brought that was new, and there you will find things only evil and inhuman, such as his command to spread by the sword the faith he preached." - Manuel II Palelologus
Would returned items that are resold be taxed? When the item is returned for a refund, would the tax also be refunded?