Not at all. Retailers typically don't pay commissions until a site generates a certain amount of business. Charitymall and 4Charity offer a specific list of choices. At iGive, you can choose any group you like. Give 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.
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. Give, by contrast, says it has an angle that makes the donations deductible to you. I hope you don't feel that your duty to charity is met by a shopping spree. If you really want to help a good cause, write a bigger check yourself.