Is the Web the gift that keeps on giving, or are you kidding yourself when you Christmas shop on a “charity mall”? There’s no clear answer, but I can think of some hard questions you should ask.

The number of charity malls has exploded this year. They promise to give to a charity of your choice if you’ll buy from an online retailer they promote.

The malls carry lists of participating merchants. You log onto the mall and click on a store’s name, which takes you to the merchant’s retailing site.

If you buy something there (and if the mall is sending the store enough customers), the merchant will pay the mall a referral commission. Commonly, it’s 5 percent to 10 percent of your purchase price.

The charity mall then donates to a public-service group. Some malls contribute just 50 percent of their commission, but competition is pushing them toward paying 100 percent.

Three malls claim they pass on the full amount: Charitymall.com, 4Charity.com and iGive.com. (iGive says that it keeps a merchant “transaction fee,” which it doesn’t count as part of the commission.)

How do charity malls make money? They sell ads. They sell general data about their members’ shopping and online browsing habits. They take fees from sponsors and merchants. They sell services to charities. They may charge charities a fee to be listed on the site.

It’s not clear that these malls can make enough money to survive.

“There will be a lot of dropouts and mergers,” predicts Alison DaSilva, vice president of the Boston consulting firm Cone Inc., which has surveyed e-charity sites. When a site fails, any commissions in the pipeline will go to creditors, not charities.

Charity shopping doesn’t cost you any more than regular online shopping, DaSilva told my associate, Dori Perrucci. You get to feel good, and the charity may pick up a few bucks. At 4Charity.com, you can even see the size of the commissions that each merchant apparently pays.

But the Web is a trust-me business. There’s no regulation and little accountability. You don’t know if all the charities got paid the right amounts, or even if they got paid at all.

While iGive.com lists checks it sends to charities on its Web site, most other sites tell you nothing at all.

Here are some questions to ask about shopping for charity:

– Do you generate a donation every time you buy? Not at all. Retailers typically don’t pay commissions until a site generates a certain amount of business. You and your fellow shoppers might have to buy $3,000 or $5,000 worth of books, sneakers or T-shirts before your favorite charity sees a dime.

– How much do the charities get, in dollars? “A lot of times, very little that’s one of the weaknesses,” DaSilva says. Take a store that pays a 5 percent commission on a $50 order. That means $2.50 for the charity mall. It takes $1,000 worth of shopping to produce $50 in potential donations. The mall might not send out any checks for less than $5.

At iGive.com you can see the size of the checks that are going out. Of the first 100 organizations on iGive’s list, 73 received less than $20.

– Which charities can you give to? Charitymall and 4Charity offer a specific list of choices. The group has to be a bona fide tax-exempt organization registered with the IRS.

At iGive, you can choose any group you like. Among the small organizations getting a nod: The American Domestic Skunk Foundation, 24 Carat Ferret Rescue and Shelter, and the Greater Latrobe Marching Band Parents Association.

However, iGive accepts any group; it doesn’t have to be a registered tax-exempt nonprofit. Outside donors have no way of telling if the group truly does what it claims.

– Do you get a tax deduction? Not by shopping through a mall, says Charitymall. You haven’t made a direct donation to the charity, so you can’t write anything off on your tax return.

By contrast, iGive says it has an angle that makes the donations deductible to you. (The lawyers who gave the opinion concede that their idea hasn’t been tested.)

I hope you don’t feel that your duty to charity is met by a shopping spree. For a charity, a $20 check is better than a poke in the eye, but not much. If you really want to help a good cause, write a bigger check yourself.

Syndicated columnist Jane Bryant Quinn can be reached in care of the Washington Post Writers Group, 1150 15th St., Washington D.C. 20071-9200.