Giving to charity has its perks, and this year that includes coupons for your favorite store. But caveat emptor: The biggest benefactor might be the retailer.

Looking at dismal sales predictions for the holiday season, shops are stepping up their links to charitable groups as a way to bring in customers. CB2, a sister to Crate and Barrel, is offering a 15% off coupon for shoppers who bring in five nonperishable food items. Purchases made during Gap s four-day Give and Get promotion yield a 30% discount for the buyer, while their choice of charity gets 5% of the total spent. (For more details on these and other offers, see the chart below.)

Consumers who sign up of course increase store traffic, while the store snags a juicy tax deduction for all those contributions. It s a feel-good move, says Ellen Davis, a spokeswoman for the National Retail Federation, an industry group. Shoppers feel like they can really maximize their spending and give back.

Here s how to navigate these offers:

Read the fine print. Check how much of your purchase is actually going to charity to gauge the promotion s worth, advises Larry Chiagouris, a marketing professor at Pace University in New York City. A shopper would need to spend $250 at Macy s this holiday season to break even on the $25 enrollment fee for the retailer s Thanks for Sharing program, $10 of which goes to charity. Infrequent Macy s shoppers may benefit more from a straight donation.

Consider need. If you have a choice, consider sending your contribution to food banks, homeless shelters and other human services groups aiding people in need, says Sandra Miniutti, a spokeswoman for independent charity evaluator Charity Navigator. Such nonprofits have seen demand for their services skyrocket with rising unemployment and other fallout from the recession. Giving hasn t increased enough to offset that, she says.

Make your own donation. Don t let store promotions substitute for your own direct contributions. A tax deduction can be as valuable as a store discount. If you want the deduction, you ve got to write your own check, says Miniutti.