Now wonder why both online versions of H&R Block's TaxCut and Quicken's TurboTax do not want you to pay the tax preparation fee upfront. By deducting the fee from your tax refund, these shops are positioned to make $20 or $30 more. H&R Block is especially sneaky by putting this "Simple Pay" as the default choice.

Both TurboTax and TaxCut are cleverly designed to let consumers fill out most of the paperwork before paying anything, a “try it for free” model. That's good, because you can see if the interview-style tax preparation system works for you ("OK -- now tell us about any investment income you have."). Payment is only required when it's time to print or e-file the forms you've been working on.

On the other hand, once you've done all the work clicking around in one of these sites, of course you are likely to whip out your credit card and pay. And I hope you do.

Because each of these programs offers a silly benefit that lets you pay for their software through a deduction in your refund. That would keep you from having to pay with a credit card, but it's a costly error. TurboTax charges $29.95 for this service; H&R Block charges $19.95.

At Block, the "Simple Pay" service fee is checked by default, making it easy to accidentally fork over the extra $20 right as you are about to file. That's a 66 percent increase in the cost of the software, for nothing.

At TurboTax the fee is even higher -- $29.95. The good news is, it's not selected by default. The bad news is filers are presented with two buttons, and "Deduct From My Refund" is about twice the size of the alternative. To its credit, Turbo Tax puts the word "additional $29.95" in bold in the explanation on top of the page. Still, I suspect some people don’t quite realize what they're doing and how much they are paying when they selected the refund deduction.