Here are some stories involving people who lost big by taking their eyes off the ball.

David is a Bell Canada customer, who called recently to ask about his latest statement. The agent told him that an item called "residence telephone" was a $6.20 a month charge for the rental of a rotary-dial phone he never had.

When he asked for his money back, Bell offered six months. He eventually settled for a refund going back three years, even though the error went back 20 years, because he realized that he should have spotted it sooner.

Fred, a Rogers customer, made a discovery when calling to check on his cable TV bill. He learned that PVTV at $16.95 a month was not for his personal video recorder (PVR), but for a channel to which he didn't subscribe.

I felt this was unfair because the coding on his bill was so mysterious. With my help, Fred got a refund going back one year (still less than what he had been overcharged). Lesson learned, he told me, saying he'd check his bills more closely from now on.

Tony collects Aeroplan miles. He didn't know he could lose them if he failed to collect new ones or redeem them for rewards over a one-year period. The rules were changed in 2007, but he only found out this year when Aeroplan sent him an email warning.

Luckily, his reward points remained intact, but his wife lost hers. He thinks Aeroplan should dump its inactivity policy or, at least, use regular mail to warn members about it.

Aeroplan has another rule you should be aware of if you joined before 2007. There's a seven-year expiry date that kicks in on Jan. 1, 2014. If you haven't redeemed your points by then, you could lose them.

Other loyalty plans have similar restrictions. The Shoppers Drug Mart Optimum card has a one-year activity rule. The MBNA Sony MasterCard requires you to redeem points for merchandise within five years or risk losing them.

How can you avoid getting fooled by mystery charges or rules that catch you unaware? And how can you avoid getting shortchanged on a retroactive refund?

One, call the companies you deal with regularly to ask about items you don't recognize. Two, always read the terms and conditions of any loyalty plan or credit card you have. They're usually found in small print at the company website.