There's no question that doing taxes yourself can save money. A 2016-17 survey by the National Society of Accountants said tax pros charged an average of $273 to prepare a Form 1040, Schedule A, and a state return. That's no small chunk of change, especially when it’s so cheap (or for some filers, free) to use a guided tax-preparation program online. Unfortunately, going it alone can be extremely costly in the long run if it leads to avoidable errors or omissions that leave money on the table or pique the interest of the Internal Revenue Service. Read on for potentially tricky situations where using a tax pro might make sense.