Why you may have surprise loot from Amazon or Barnes & Noble

For book lovers, this week may be as thrilling to them as when Harry Potter received his invitation to study at Hogwarts School of Witchcraft and Wizardry.

The reason? Surprise credits awarded by Amazon (AMZN) and Barnes & Noble (BKS) to many e-book buyers this week as part of a settlement of a price-fixing suit against some publishers brought by the federal government.

Both Amazon and Barnes & Noble alerted customers about the credits on Tuesday, which means you shouldn't automatically toss emails from the retailers into your trash bin. Part of the fun of receiving a credit appears to be comparing settlement amounts, with Twitter lighting up with customers bragging -- or poking fun at -- their new-found book money. So far, the amounts range from a low of less than $1 to more than $200.

What to watch out for? Amazon's email bears the subject line, "eBooks Antitrust Settlement Information," while Barnes & Noble's email reads, "Important Information about Your Settlement Credit."

Even if you miss the email, the credit will be sitting in your account.

There are a few catches, however. On Amazon, the credit is good until March 31, 2015, while Barnes & Noble's credit expires April 1, 2015. The credit is also limited to purchasing e-books or print books, which rules out buying, say, the third season of HBO's "Game of Thrones."

The credits are based on the number of books a person purchased during the claims period -- between April 2010 and May 2012 -- as well as whether the book was a New York Times bestseller. For books on the bestseller list, the refund amount was $3.17, while other books were awarded a 73 cent refund. The credits stem from a settlement between the government and publishers accused of conspiring with Apple to fix e-book prices, including Hachette, HarperCollins, Simon & Schuster, Penguin and MacMillan.

Oddly, Minnesota residents received a larger refund amount because claims for residents of state were settled through separate negotiations. Residents there are entitled to $3.93 for New York Times bestsellers and 94 cents for all other books.

And for those who are pleased but not sure of what to buy, everyone from Businessweek to authors on Twitter are full of suggestions. Of course, it's likely that most readers already have a long string of titles on their wish lists.