You can claim yourself as author on any PLR product, but some authors do not want their work to be copyrighted in it's exact form as they originally created it.

For instance, if you change the graphics, or alter the product's content significantly you can then claim full copyright.

All resellers should use good common sense, and consideration for another persons work. After all, the author is doing large amounts of work creating products, and has been gracious enough to allow you to also profit from their work, making it a priviledge for you to sell the product, not a personal right to sell it.

Note: Most resale products are not copyrighted material, but the right of intellectual property rules do apply. Meaning that the original author may not have vistited the copyright office for their product, but they can indeed prove that they did create the product and can prove it.