By LIZ VACCARIELLO , Reader's Digest:

" Good Morning America" is teaming up with Reader's Digest on a special series, " 13 Things Experts Won't Tell You." This month, Reader's Digest unveils the 13 secrets your shoe salesman won't tell you on how to find the best deals in the store and the perfect fit, plus six bonus tips.

1. I may be kneeling at your feet, but I'm not your servant. Lose the 'tude, dude.

2. Don't ask for a size 7 if you're a 9. No one cares how big your feet are (though we all appreciate a little foot powder, if it's not too much trouble).

3. Shoes should be as wide as your feet and longer than your feet. It's not just the distance from the heel to the end of the big toe that matters. It's also the distance from the heel to the ball of the foot.

4. Don't try on sample shoes if they're not your size. "People smash their feet into shoes that are three sizes too small, and then I have sample shoes that have been stretched," says a New York salesman.

5. Please don't keep me waiting ten minutes while you talk on your cell phone. What if I did that to you?

6. If we don't have exactly what you want, it may not exist. And I can't cobble it together in the back room while you wait either.

7. Losing weight will make your knees, ankles, and feet feel better. Shoes-not so much.

8. The metal gauge that measures the width and length of your feet is called a Brannock Device. Tell your kids it should stay flat on the floor and not go hurtling through the air toward my head. Many thanks.

9. Don't be a serial shoe returner. Once or twice, okay. But 10 or 20 times a year? I don't think so.

10. If we tell you that a shoe isn't a good fit, take our word for it. Customers have been known to try on a shoe that's too small, and then they can't get it off.

11. I've spent 30 minutes with you, and then you tell me you need your wife's approval? News flash: She doesn't need yours. Next time, bring her along.

12. You get what you pay for: A $20 shoe isn't going to feel-or last-like a $120 shoe.

13. Do you really want to borrow one of the store's footies to try on shoes? The ones in that box? The ones that everyone in town has used? The ones that haven't been washed since I started working here? (I didn't think so.)

BONUS TIPS:

14. Don't fall for prices ending in 9, 99 or 95. These so-called charm prices make us think they reflect deals. We also tend to round them down, reading a price like $5.99 as $5, a phenomenon known as the left-digit effect. William Poundstone - the author of "Priceless: The Myth of Fair Value (and How to Take Advantage of It)" - also notes that markdowns don't often include these magic numbers. That's because when the discount is easy to calculate, we think it's a better bargain. Thus "Originally $20, now $15? works better than "Originally $20, now $13.97." You'll be more tempted to go with the former, even though the latter saves you more.

15. Know you're being tracked. If you use a store loyalty card, your buying habits are being recorded and often used to lure you to buy more. According to the New York Times, retailers these days are successfully tricking consumers into spending more by determining their spending "sweet spot," based on previous purchases.

16. Understand how certain phrases are used by retailers. "For a limited time only" creates a sense of urgency, says Yale marketing professor Ravi Dhar tells mainstreet.com. And retail analyst Amy Noblin theorizes in USA Today that the come-in, "Buy one, get one 50 percent off," incites more people to buy than if the sign reads simply "25 percent off everything."

17. See per-customer limits for what they are: a ploy. As Vicki Morwitz of New York University's Stern School of Business explains to cbsmoneywatch.com, "[People] think, "Oh, this is scarce, I should buy this,' when it's probably not."

18. Don't try on clothes/shoes you don't need. A shopper who stops to chat with a store employee and tries something on is twice as likely to buy as a shopper who does neither, Paco Underhill, author of Why We Buy: The Science of Shopping, tells time.com.

19. If you're a guy, shop alone. According to a Journal of Marketing Research study reported by money.com, a full 56 percent of men shell out more if they hit the mall with a friend as compared with women, 4 percent of whom actually racked up bigger receipts when going solo. That's because when men shop, they like to show off their knowledge and status via their purchases.