When an 84-year-old woman in California decided to hire a ventilation company based on a price of $59.95 for “unlimited” duct cleaning, she probably had no idea that she would end up stuck with a bill that was more than 25 times larger than what she’d been quoted.

CBS 5 in San Francisco looked into the matter and found several questionable issues with the bill — for instance, most of the writing on the bill is completely illegible. Then there’s a $650 charge for installing a UV light in the woman’s utility closet. The bill also doesn’t add up. Based on what the reporter could make out, the total is $100 higher than the tally of all the charges.

“She was overwhelmed,” says the woman’s daughter. “She said they were talking too fast and doing things as they talked.”

After seeing the bill, the daughter tried to have the company remove the unnecessary UV light but was told “We can’t do it. Once it’s installed, it’s yours.”

Since then, the company isn’t returning calls from either the customer or CBS, which found that at least three companies — one in California, one in Chicago and one in Washington state — that all use the same 800 number. Two of these businesses have “F” grades from the Better Business Bureau.

Here are some of our tips for preventing this kind of scammy behavior:
1. Get The Quote In Writing
Not only should you get the quoted price in writing, you should also get a written assurance that no additional services will be performed without written approval and a price quote.

2. Research The Company
A simple Google search can tell you a lot about a company. Check for online reviews at sites like Yelp, and look to see if the company has a record with the Better Business Bureau. If you have trouble locating any information about a business, you may want to reconsider.

3. Have Someone With You
If you can, have someone with you in your home when workers are doing their job. Having another person around means more eyes on the work being done, and another person to back you up if you think you’re being scammed. It’s harder for a scammer to convince two people that they should pay for services they don’t need.

Want more consumer news? Visit our parent organization, Consumer Reports, for the latest on scams, recalls, and other consumer issues.