Experts share proven tips and their five favorite comparison shopping sites to help you get the perfect product at the right price.

If you’ve ever bought something online, then you’ve probably used a comparison shopping site or app. After all, if you type “comparison shopping” into a search field, you’ll receive no less than 4 million results. About $1.5 billion in merchandise is sold in the U.S. through these engines. For retailers, they often translate directly to the success or failure of a product line, as anywhere from 5 percent to 50 percent of their total sales are based upon comparison sites, according to CPC Strategy, which specializes in online search marketing consulting for the retail industry.

Purchasing what you’re seeking for as little as possible, however, requires more than a few simple clicks. So consider the following advice from consumer experts to get the most out of your efforts:

Understand that not all comparison shopping sites are the same. That’s why it’s recommended to search for a product on more than one—if not many. Online vendors change prices frequently, and one comparison site may have the most recent discounts, while others may not. “You need to go to multiple ones to ensure you’re getting the best deal,” says Andrew Schrage, co-founder of MoneyCrashers.com, a personal finance site that covers family/home items and lifestyle products, as well as credit/debt and investing advice. “For example, I just did an Internet search on a specific webcam on two engines. One gave me a lowest price of $67.99 and another’s lowest was $59.99.”

Make sure it’s secure. Regardless of how much you trust the comparison shopping site, you typically will be taken to a vendor once you make a final purchase choice. If the vendor is new to you, you’ll want to verify the security level of your transaction. “You want a site that encrypts data during transmission,” says Michael Lerner, publisher of LearntheNet.com, a leading producer of guides to smart Internet usage, one used extensively by thousands of schools, universities and libraries worldwide. “You know it does if there’s a ‘lock’ icon on your web browsing window. And the web address should always begin with ‘https.’ ”

Evaluate more than cost. What good is a bargain item if it never arrives? Or is shipped in poor condition? In addition to the security of your personal information during a transaction, you need to check out the lowest bidder’s service reputation via reviews and searches. “Some businesses are more reliable than others,” Schrage says. “Be sure to do your homework before pulling the trigger.”

Even if the merchant’s reputation is excellent, something could still “go wrong.” So, as a precaution, pay with a credit card that allows you to challenge charges. “In addition, print a copy of your order for your records,” Lerner says, “and make sure there’s a link to a page where you can track delivery status.

Use engines to enhance your offline shopping. If you’re looking for items at a brick-and-mortar retailer, you can still take advantage of comparison sites. Crosscheck the in-store price with what’s being offered on the shopping engines. In many cases, the in-store merchant will meet the best online deal you can find. “You can also use your smartphone to ‘comparison shop’ with local competitors while in a store,” Schrage says. “I like an app called RedLaser. You simply scan the barcode of an item, and it will tell you whether a nearby business has it for less. What’s more, it will give you driving directions if you need them.”

Don’t forget about shipping. The sales price represents only part of the cost. You’ll want to get the best shipping option as well, given how much this expense can drive up the total bill. Of course, there are always services such as ShopRunner.com and Amazon Prime, which offer free, two-day shipping for an annual fee. (For ShopRunner, the fee is $79 a year. For Amazon Prime, it’s $99.)

As for which comparison engines are considered among the elite? The following have been ranked by MoneySavingPro.com as the top five, taking into account the selection; the timeliness and accuracy of deal information provided; the trustworthiness of the vendors; the overall user experience; and quality of customer service.

1. Pricegrabber.com: Gets outstanding marks for its wide range of vendors and items, along with up-to-date deals and its “Grabworthy” section, which posts topic-specific articles (such as baby products for new parents) to help you make informed choices.

2. Yahoo! Shopping: Offers a huge range of retailers with ratings/reviews in a simple, user-friendly interface.

3. Pronto: This site is sleek and stylish, and provides its “Sales!” link for those who don’t want to get email alerts about new retailer promotions. Instead, Pronto subscribes to all the email services and posts them at “Sales!”

4. BizRate: In addition to comparison shopping, BizRate lists dozens of businesses which are considered to be highly trustworthy with its “Circle of Excellence” designation.

5. NexTag: Somewhat of the ‘granddaddy’ of comparison shopping, NexTag has been around since 1999, which speaks to its commendable track record of credibility among users.