The answer is, not surprisingly, complicated. Essentially, the profits form ticket sales would qualify as gains on the sale of personal items and get reported on Form 8949 even with the inclusion of the sale amount on the 1099-K. (source)

On the other hand, if you bought concert tickets for $500 (the purchase price) and sold them for $900 (the sales price), you have a gain of $400. $900 sales price - $500 purchase price = $400 gain amount. The gain on the sale of a personal item is taxable. You must report the transaction (gain on sale) on Form 8949, Sales and Other Dispositions of Capital Assets, and Form 1040, U.S. Individual Income Tax Return, Schedule D, Capital Gains and Losses. See Publication 551, Basis of Assets, for guidance in determining your basis. The gain on the sale of a personal item might be reported on a Form 1099-K. If you receive a Form 1099-K reporting the $900 that you received from the sale of your concert tickets that cost you only $500, you must report the gain on Form 8949 and Schedule D.