The law may vary from country to country, but I think it doesn't matter if it's new or used. The scope is not a purchase, it is an income, and for any kind of income, one must pay taxes. Of course, being a used scope it can be evaluated much lower than its catalog price, but it can not have zero value, unless we play in the grey area.
In some places, this is even worst. This kind of win will be considered a lottery type income. For a lottery win, the tax is even higher, usually somewhere between 25%-40% instead of the 16% used in that best case scenario calculation. Anyway, the taxes vary widely across the world, and I'm not a bookkeeper, so I might be totally wrong.
Before taxes, one need to win in the first place, so good luck to everyone!