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Most people pay someone to do their taxes for them. But, as one expert points out, there are plenty of mistakes people make when choosing a tax preparer.

"I think the biggest one is somebody who guarantees you a refund. I mean without seeing your material. That's a mistake," says tax expert Kevin McCormally with Kiplingers.

"Somebody will go in and say I can get you a refund of $5,000 if you give me $500 of it. Never work with somebody who promises you a refund," he added.

McCormally also advises filers to not work with a tax preparer who's willing to fudge some of their numbers.

Read More: Avoiding the Alternative Minimum Tax

"I've known of preparers who will say, 'You know, why don't we put down that you took a class last year to improve your job skills,' and the taxpayer said, 'But I didn't,' and they said, 'Well, the IRS will never catch you,'" he tells ABC News Radio.

Another tip to keep in mind: It's illegal for a tax preparer to charge you a percentage of your refund. You also want to avoid anyone who doesn't have a Preparer Tax Identification Number.