13 tricks retailers use in stores and online to make you overspend - and keep coming back for more

Business Insider previously reported on how a one-click checkout process (like on Amazon) can encourage overspending.

Because you don't need to enter billing, shipping, or credit card information, there's no immediate obstacle to buying whatever you want or need. That's great if you're in a rush — but not so great if you're on a budget.

Free shipping should be good for our wallets — after all, it means cutting the overall price of a purchase.

Alas, it's not always.

If the free-shipping threshold is, say, $50, you're more inclined to try to spend $50 (instead of the smaller amount you were planning to spend) so you can get them delivered gratis.

Somewhat counterintuitively, "Most people would rather spend more money buying things they don't need than pay for shipping costs," money-saving expert Andrea Woroch previously told Business Insider in an email.

ProPublica reports that the reason eye drops overflow your eyes is because drug companies make the standard drop larger than the human eye can hold at once. In other words, you're throwing money away every time you buy a bottle of eye drops because half the liquid is wasted.

Companies with free-return policies (think Zappos) aren't just nice — they're smart.

One 2012 study, published in the Journal of Marketing, looked at customers' habits over roughly 49 months at two major online retailers. Results showed that after free-return shipping policies began, average spending per customer increased by about $620 over two years at one retailer — and by about $2,500 at the other retailer.

In January 2018, Google debuted a new feature that would allow users to mute "reminder ads" on websites and in apps. Reminder ads are those advertisements for shoes — or any other product — that have been following you around online since you checked them out a few days ago.

One caveat: You can't turn off all reminder ads automatically; you have to opt out of them on a case-by-case basis, The Guardian reported.

That means you may still be haunted by the ghost of those shoes you sort-of-wanted-but-didn't-really-need — and depending on how much willpower you have, you may cave and buy them.

On a Reddit thread dedicated to sharing tricks that store owners use to get customers to spend more money, beast77 wrote: "My dad owns a college bar in Lincoln NE, and he uses bigger straws to get people to drink faster, and then buy more drinks."

It's not just your imagination.

As Business Insider's Kif Leswing reported, "Apple is limiting how much power an iPhone processor can draw in certain circumstances, therefore limiting the processor's peak performance."

According to Apple, the reason for this is that it's controlling how much power older phones can draw so the phone doesn't suddenly shut down.

How can you solve this problem? Buy a new one.

A logical theory is that buying in bulk saves you money. A single loaf of bread might cost $4, but five loaves of bread might cost $15.

That's $5 saved, right?! Not so fast.

According to a study led by Victoria Ligon at the University of Arizona, consumers try to food-shop for the week or two ahead, when in reality, we don't plan that far in advance. So we end up ordering takeout or meeting up with a friend, and all that bread we bought ends up going stale.

"All of our food promotions are designed to get people to buy more," said Anita Bhappu, Ligon's advisor. "We believe it's cheaper if we buy more now, but we rarely take into account how much we throw out in the end. And if you factor in the cost of what you are throwing away, it is very unlikely that you are saving anything."

Expiration dates have gotten a lot of attention in recent years, as people have started to realize that you don't have to throw food away (wasting money in the process) just because the "best by" date has passed.

According to the USDA, food dates refer to product quality, not safety — except in the case of infant formula.

From the USDA website:

• A "Best if Used By/Before" indicates when a product will be of best flavor or quality. It is not a purchase or safety date.

• A "Sell-By" date tells the store how long to display the product for sale for inventory management. It is not a safety date.

• A "Use-By" date is the last date recommended for the use of the product while at peak quality. It is not a safety date except for when used on infant formula as described below.

The "rinse" step? Necessary — you don't want to show up to work with suds in your hair.

The "repeat" part? That's mostly a waste of time and money.

"Do not rinse and repeat. Usually one shampoo is efficient enough to wash away build-up," celebrity hairstylist Sarah Potempa told TODAY.

We're more inclined to purchase something if we think it might be gone tomorrow. Psychologists call it the scarcity principle, or the scarcity heuristic.

Business Insider previously reported on a classic study published in 1975 in the Journal of Personality and Social Psychology, which illustrates this principle in action. A total of 200 people were presented with either a jar with 10 cookies or a jar with two cookies. Results showed that people consistently rated the cookies in the emptier jar as more valuable.

Outside the laboratory, if you find out a pair of shoes is on sale today only, you're more likely to snap them up than if you think they might be discounted for a while.

Technically, you're under no obligation to buy anything that you taste in the supermarket. But retailers know how guilty you may feel if you don't.

Psychologist Robert Cialdini calls it the "rule for reciprocation": If someone does something nice for you, you're more inclined to do something nice for them.

In a 2002 study published in the Journal of Applied Social Psychology, customers who were offered chocolate by their waiter tipped up to 21% more than customers who weren't offered any chocolate.