Written by Sally Wadyka

Grocery shopping seems like a harmless enough activity. It’s a chore, but it’s one that most of us do at least once a week, without giving much thought to what’s going on behind the scenes at the supermarket.

How we shop has become a science that’s studied endlessly. “Market researchers have worked for years to come up with ways to make sure shoppers see as many products as possible, because the more they see, the more they buy,” says Marion Nestle, author of What to Eat: An Aisle-by-Aisle Guide to Savvy Food Choices and Good Eating.

So to make yourself a smarter shopper, learn about the top tricks and other secrets lurking at the supermarket.

1. The shopping carts have cooties.

According to studies done on shopping carts, more than 60 percent of them are harboring coliform bacteria (the sort more often associated with public toilet seats). “These bacteria may be coming from raw foods or from children who sit in the carts,” says Chuck Gerba, Ph.D., a microbiologist at University of Arizona. “Just think about the fact that a few minutes ago, some kid’s bottom was where you are now putting your broccoli.” According to studies done by Gerba and his colleagues at University of Arizona, shopping carts had more bacteria than other surfaces they tested-even more than escalators, public phones and public bathrooms. To avoid picking up nasty bacteria, Gerba recommends using sanitizing wipes to clean off cart handles and seats, and to wash your hands after you finish shopping.

2. Dates are open to interpretation.

Except for baby formula and food, product expiration dates are not required by Federal regulations (some states, however, have their own rules requiring product dating). Labels that give a “Best if Used By” date are more of a suggestion than a safety issue-the food will taste best if eaten by the date on the label, but won’t necessarily be unsafe if eaten after that. If a product is stamped with a “Sell-By” date, that is how long the store should display it. Once you bring it home, perishable products (like meats) should be kept refrigerated and used within a few days. For more detailed charts explaining the shelf life of various products, go to USDA Food Safety and Inspection Service.

3. Kid-friendly food is purposely placed within their reach.

Anyone who shops with a child (or several) in tow has to keep an eye out for products the kids grab and toss into the cart. “I always tell parents never to bring a kid to a store,” says Nestle. “The packages with the cartoons on them are often placed on low shelves where even toddlers can reach for them.” A trip down the cereal aisle will confirm this. “Sugary cereals are at kid’s eye level, while the healthier, all-bran options are usually on the highest shelves,” says Tara Gidus, R.D., a spokesperson for the American Dietetic Association. It’s the same situation at the cash register, where candy and gum are strategically placed to encourage impulse buys by adults and kids can easily grab low-lying products.

4. They cut up food so they can charge more.

In the produce department there are luscious-looking slices of pineapple and melon, veggies cut up and ready for cooking or salads. At the meat counter, chicken breasts and beef are cut into chunks and marinated-ready for immediate grilling. There’s no denying that these pre-cut foods can make life incredibly easy. And nutritionists agree that if they get people to eat more healthfully, there’s nothing wrong with them. But realize that you’re also paying a tremendous premium-sometimes up to twice as much as uncut versions of the same food-just so you don’t have to bother picking up a knife.

5. Good-for-you foods require bending and reaching.

Not surprisingly, grocery store eye candy (which sometimes is actual candy)-those foods with enticing come-ons and delectable photos on the packaging that aren’t on your shopping list-are prominently placed to encourage you to reach for them. Even in the pasta aisle, you’ll find the most popular noodles (including packaged mac and cheese) at eye level. Look up to the highest or lowest shelves if you want to find healthier whole wheat options.

6. End-of-aisle displays are there to distract you from your mission.

“Food companies pay the stores to place their products where they can be seen most easily-such as in a display at the end of an aisle,” says Nestle. That prime real estate is likely to hold high-profit items or grouped items (such as marshmallows, chocolate bars and graham crackers for s’mores) designed to inspire impulse buys. And although sometimes those aisle-ends are used to promote sale items, we will buy even when there is no discount. “People are 30 percent more likely to buy items on the end of the aisle versus in the middle of the aisle-often because we think what’s at the end is a better deal,” says Brian Wansink, Ph.D., director of the Food and Brand Lab at Cornell University and author of Mindless Eating.

7. Bargains aren’t always a bargain.

Who can resist an offer like “buy five, get one free,” or “three for $1”? Apparently, very few people can. “Any time you see numbers in a sign, you’re likely to buy at least 30 percent more than you may have purchased otherwise. “So if you go looking for soup and the sign says “limit 12 per person,” chances are you’ll purchase several more cans than you intended to buy,” he says. And of course, if you buy more than you need, it’s not necessarily a bargain. Or worse yet, it could lead to over-indulging. “Mindless shopping leads to mindless eating,” says Wansink. “Once the stuff is in the house, you’ll eat it whether you really want it or not.”

8. You’ll walk the store the way they want you to.

There’s nothing haphazard about the layout of your grocery store. Sure, some of it is practical (like refrigerated cases along the periphery or meat cases in the back by the store’s loading dock), but some is carefully calculated to help you part with more money. Walk in the front doors and chances are you’re faced immediately with hard-to-resist items (not on your list) like fresh-cut flowers or just-baked loaves of bread. Just try walking past them en route to a carton of milk without tossing something extra into your cart. In fact, research has shown that 60 percent to 70 percent of what ends up in our carts is unplanned.

9. The salad bar can make you sick.

Raw produce at the salad bar, pre-made salads at the deli counter and other pre-cooked prepared foods all have the potential for harboring harmful bacteria (like E. coli, salmonella and Norovirus). “The biggest contributors to unsafe food are foods that are held at unsafe temperatures, handling of food by individuals with poor hygiene, and refilling partially used containers of perishable food with fresh food,” says Michael Doyle, Ph.D., director of the Center for Food Safety and Quality Enhancement at University of Georgia. He recommends that consumers pay attention to cleanliness, freshness (all prepared food should be thrown out if not sold by the end of the day), and way food is stored (cold foods need to be kept at 41 degrees or below; hot foods at greater than 135 degrees). As for those bulk bins of candy and trail mix-while it might be a bit gross to think about people reaching in and “sampling” the goods with their dirty fingers, according to Doyle, the risk of catching anything from them is very low. “Harmful microbes are not likely to grow in bulk-bin foods because most of those foods do not contain enough moisture to support microbial growth,” he says.

10. They don’t always clean as often as they should.

Health inspectors routinely visit supermarkets to look out for the red flags that may signal unsafe conditions for your food. But you can do a little snooping yourself. Flies in the produce or meat departments could be depositing bacteria on raw food. Roaches scurrying across the floor could also be harboring dozens of different diseases. And of course, check the shelves and products for dirt and grime-cans that are covered in dust may be an indication that they’ve sat around past their shelf life.