Bookstores
You received a book as a gift. You know you’ll never read it and it isn’t covered in soy sauce—yet—so take that sucker to a chain bookstore for an exchange. Even if you don’t have a receipt, as long as the book is in stock you can trade it for instant store credit. The book will be scanned at the register and you’ll be given the lowest price the book has been sold for over the past six months, or, if you’re really lucky, the book will scan at full cover price. If you have the patience (and the barefaced cheek) to ask, some stores will mail the credit as a gift certificate; then you can spend your ill-gotten gains at the café. Shadier still: If you scour the street book vendors you can find titles for way cheaper than the cover price—and then return them. For example, a $5 Spanish dictionary could be exchanged for $9 credit.

Craigslist
Missed Connections might get you laid, but flipping concert tickets on the site could give you a much more satisfying rush. Buying four tickets to the Beastie Boys last summer would have cost you $200. Reselling them four days later could have raised $400. And the purchaser comes to you—with cash. Obviously the trick is knowing which shows will sell out—the Beasties playing Brooklyn is a no-brainer—so do your homework, keep an eye out for breakout bands playing smaller venues and monitor fan sites for tip-offs. Fail, and you could find yourself begging three friends to see Coheed and Cambria or eating the cost.

Banks
They’re on every corner and often they’ll pay you to open an account. Bank Bonuses (bankbonuses.info) lists all kinds of special offers, such as $25 cash incentives from the likes of HSBC to lure current customers into switching to online bill payment. We found a tasty deal at Bank of America: Open a new checking account with $100, maintain it for one year and they’ll give you $100 (the offer runs until February 29, but call and check to see if your branch has the offer). Take the money and run.

Movies
Too cheap to pay full price at the movies? Buy children’s tickets—they look so similar to adult tickets that you’ll sail straight into that R-rated film without a guardian. Shadier still: Get several friends together and buy two tickets. Most theaters will let you come and go as long as you are holding a stub, so have two people go in with everyone’s bags. Then one comes back out with both stubs and returns with another friend. Repeat as many times as you can get away with. Use the stubs to sneak into a second showing and it’s an even sweeter deal.

Credit cards
Mileage is old news and money back can be small change, but hotel rewards are seriously useful. On CreditCards.com, we found that applying for a Chase Marriott Rewards Visa bags you 20,000 bonus points—and a gratis sleepover at certain hotels. A mere 18,000 points gets you a $50 voucher toward anything Marriott offers (that could be a free dinner or facial, even one night at Fairfield Inn). Talk a friend into doing the same, and you can enjoy an overnight stay at the Times Square location for 40,000 points. And if you cancel the card and wait two years, you can apply all over again. Sign up for the One from American Express card and get $50 two months after your first purchase. If you want to be all classy, apply for an AmEx Gold Card. They’ll give you 10,000 reward points; that’s a hefty $100 in gift cards.

Department stores
Here’s a reason to brave the semiannual sales at major department stores. Purchase a heavily discounted item, then wait until the sale is over and return the item, sans receipt. Instead of getting store credit, ask them to refund it to your store card (which you sign up for right there at the checkout) and you’ll get credit for the full-priced item. Shop yourself silly with the difference. Shadier still: Wait a few months, for the store to send you a check to cover the negative balance on the card.

* Probably. Certain activities listed here are morally questionable and possibly illegal; these ideas are for entertainment purposes only.