Don't be like Ironman! Don't get fined for falling foul of America's "sweepstakes" laws.
Call it a "contest", but if one is not careful, the "contest" might be a lottery or sweepstakes, and it might be illegal if one does not know what one is doing... and many authors don't. They are simply keen to promote their books and their brand, attract massive followings on social media sites, and make a prestigious list.
Whether the quid pro chance-at-a-quo (or price of entry into a contest) is signing up for a newsletter, or giving a "like" on a site, becoming a "follower", quoting a quote, posting a review, or paying a fee, the "quid" is a thing of value, at least to the author.
The "quo" is the chance to win something, which might be money, a gift card, a token, an ebook, a signed paperback or hardback, a necklace, a bundle of books, even an ebook reader.
The fact is, for the contest to be legal, one must offer a free, alternative way to enter, such as mailing in one's name and contact information on a postcard.
All the best,