From youhoo.com: If  plan to have your taxes done by a professional tax preparer you'll want to keep these red flags in mind.

• Guarantee you'll get a refund.
• Get paid by charging you a percentage of the refund.
• Don't ask you for supporting documents, such as your W-2 or 1099s.
• Offer to create documents to support false or exaggerated deductions.
• Ask you to sign a blank form that they will fill in later.
• Refuse to give you a photocopy of your return.
• Refuse to list his or her Social Security number and sign the return, as required by law.
• Aren't available year-round. (Some preparers set up shop during the mad tax rush and then sort of disappear.)