My wife had a similar experience. We both grew up in a small city, and throughout her life she never had a single cavity. She prides herself on the health of her teeth.
In college we both moved to a larger city (which has a more competitive dentistry market), and suddenly dentists were finding cavities every time she went for a checkup.
While it's entirely possible that she didn't have cavities before, and now does all the time, I feel like the competitiveness of the market here has lowered the standard of what actually requires a filling.
That is, in our hometown, a dentist could take a more measured approach -- if something looked like it could develop into a problem but wasn't currently one, they had the leisure of waiting for the next six-month checkup to reevaluate. Here, it seems to be the equivalent of shoot first and ask questions later.
Also, every filling I've ever had never came as a result of actual pain or discomfort, they only occurred because I went in for a regular six-month checkup. Given my wife's experience (going from apparently perfect teeth to requiring fillings at nearly every checkup) I can't help but feel about as confident as a woman at an auto shop hearing "You need your blinker fluid replaced".