With Black Friday fast approaching, the Federal Trade Commission is reminding shoppers to be wary of fake product reviews when buying stuff online.

But spotting phony ratings isn't always easy. And they're everywhere, skewing rankings on some of the biggest retailers, including Amazon and Walmart.

Here are six tips to help you spot fake reviews and protect your purchases.

1. Don't rely on star ratings alone

It's hard to know exactly how many online reviews are phony, but roughly 31% of reviews found on ecommerce sites like Amazon, Walmart and Best Buy are suspected fakes, according to one 2021 analysis. That means that any star rating is likely to be skewed. 

Since the average star rating can't be fully trusted, consider reading a sampling of reviews across all star ratings. This will give you a better idea of whether a product is worth buying.

2. Watch out for red flags

Fake online reviews are typically short, vague and hastily written, without a lot of concrete details about the usefulness of the product. Sometimes it's obvious, with reviews limited to something like, "I would recommend" or "great product."

Another sign of a fake review is hyperbole or excess enthusiasm, especially for mundane products like baking sheets or extension cords. Typos are also common, as many phony reviews are written overseas in countries where English isn't the primary language.

3. See if the reviewer is legit

When looking at a review, the FTC recommends checking if the reviewer has written other reviews. If it seems like they created an account just to write one review, it could be fake.

Another obvious sign of a phony reviewer is the same short review for a wide array of products.

4. Check for a burst of reviews during a short time span

Phony reviews tend to be published in bulk over a short period of time, sometimes all in the same day.

An usually high number of five-star reviews that don't say much more than "works great!" over a narrow range of dates should be considered suspicious.

5. Look out for fake negative reviews, too

To avoid detection, some phony reviews try to appear less obviously fake. This can include slightly lower ratings, like giving four stars instead of five.

And remember that not all reviews are meant to be positive. Fake negative reviews are sometimes used to harm a competitor.

6. Read independent product reviews from established sources

Aside from looking at customer reviews, consider reading product reviews on legitimate news or consumer websites, such as NBC's Select, CNET or Wirecutter.

Often, they provide comprehensive, unbiased "warts and all" reviews of products that can be more useful than customer feedback alone.

Want to earn more and work less? Register for the free CNBC Make It: Your Money virtual event on Dec. 13 at 12 p.m. ET to learn from money masters like Kevin O'Leary how you can increase your earning power.

Don't miss: This common early retirement strategy is a 'terrible idea,' says financial planner