You may think you’re finished with your 2012 taxes because the April 30 deadline has passed and your refund is in the bank.

But the Canada Revenue Agency is just getting started. The CRA assessed 13.4 million returns between mid-February and May 9, about half of the returns it will process for 2012. The average refund is $1,617.

If you filed online you probably got your tax return back in a few days. But what you might not know is that CRA pays out those refunds based on what you filed and may go back for a closer look.

The CRA won’t say how many returns it revisits each year. Some are chosen at random, but some may be selected because the CRA needs more information.

When you file electronically, as nearly 85 per cent of us now do, you don’t send your receipts — just make sure you keep them. You may get a letter from by July asking for such things as proof of charitable donations, Registered Retirement Savings Plan (RRSP) contributions or child care expenses.

“That’s not an audit. That’s a request for information. People shouldn’t fear that,” said Scotiabank tax expert Tim Cestnick, president of WaterStreet Family Wealth Counsel. “Most of the time, you’re just sending them stuff that you would have sent them anyway if you had filed by paper.”

In other cases, there are things in the return that seem out of the ordinary, for example a dramatic change in income or a large increase in deductions. Here the CRA comes looking for tax evasion and will pour over all receipts and T-slips to find out if you’ve been honest.

Related: 8 ways to get the biggest refund

These are seven factors that will typically trigger a CRA audit:

1. Being self-employed: If you own a business the CRA is more likely to take a closer look to make sure you are declaring all that you make. If you’re in construction, retail or the restaurant business — places where cash can change hands unrecorded — the odds that the CRA will flag you are even greater.

2. Any big changes: This could prompt the CRA to ask if there’s been a mistake or ask for proof that things have changed.

3. Recurring losses: The CRA may take a closer look at a business that doesn’t ever seem to make a profit but where the loss can be used to offset other income.

“Once you’ve reported losses for two or three years in a row on the same business or rental property, a little flag will go up on your tax return,” Cestnick said.

4. Big expenses: Did you really move 40 km closer to your work? Were those child care expenses incurred so you could go to work or head to the movies on Friday night? The former is deductible; the latter is not.

They also want to see your receipts. “There are situations where it’s obvious that someone incurred the cost, but they can’t find the receipt. Does that mean they shouldn’t claim it? No, claim it, but be prepared to have a battle if the CRA ever comes back and asks questions,” Cestnick said.

5. Not blending in: The CRA compares what you report against the norm for your industry, what your colleaagues report and even your neighbours. “If you’re declaring $40,000 a year income and you live on a street where everyone else makes $150,000, the CRA is going to wonder how you can live there,” said Dale Barrett, tax lawyer and author of Tax Survival for Canadians: Stand up to the CRA.

6. Aggressive tax planning: Federal finance minister Jim Flaherty said in his latest budget that he would collect millions in extra revenue by closing tax loopholes.

“If you participate in a variety of programs like tax shelters, donation schemes, any very aggressive tax planning, you will be audited, 100 per cent guaranteed. They will look into these plans eventually. It’s a matter of when, not if,” Barrett said. “Any aggressive tax planning scheme should be avoided.”

7. Home office expenses: You’re allowed to declare a certain percentage of your residence as a home office, but claiming more than 10 or 15 per cent sends a signal, Barrett said.

Related: How to avoid these 8 tax filing mistakes

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If you drive your vehicle for personal and business purposes, keep a detailed record to show which is which.

“With electronic calendars, it’s easy to see where you’ve been and with Google Maps you can keep very detailed records on how far you’re driving from your place of employment to your business appointments,” said Evelyn Jacks, a Winnipeg tax expert. “Forgetting your pencil and paper log at home is no longer an excuse.”

Being organized is the best defence. “If you’re organized and they come to audit you, it looks a lot better than if you’re scrambling around the house and you can’t find the paperwork,” Cestnick said.

If you’ve made false claims, you can come clean and reduce the penalty. The CRA has a voluntary disclosure program.

“It’s best to get everything cleaned up before CRA contacts you,” says Barrett. “If you do it this way you can save tens or hundreds of thousands of dollars in penalties just by doing it first.”

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