How reliable are those online reviews of real estate agents? A consumer group reviews the reviews.

Online reviews are a prime source of information for consumers looking for which product to buy, which restaurant to order from, what movie to watch and what plumbing contractor to hire, but reviews of real estate agents are less widely used, according to new research by the Consumer Federation of America (CFA), a national organization of nonprofit consumer groups. More often, people rely on a recommendation from a friend or co-worker, but those recommendations may be limited in value since they reflect only one person’s experience.

The CFA’s researchers compared online information, reviews and ratings on Zillow, Realtor.com, HomeLight, Yelp, Facebook and websites of real estate agents to determine which sites offer the most valuable information for buyers and sellers. Researcher Stephen Brobeck, a senior fellow with the CFA, found consumers could benefit most by learning about an agent’s experience and reading client reviews.

Brobeck found that among the sites he reviewed, Zillow was the most likely to include information on individual agent profiles about past sales (77 percent of the time) and customer reviews (61 percent of agent listings). Realtor.com was the second most likely to include past sales (55 percent of listings) and reviews (25 percent of listings). Among the key pieces of information about an agent’s listings are the date — so that buyers and sellers can know how recently the agent worked with clients — and whether the agent worked with buyers or sellers on the transaction.

Customer reviews are common on agent websites, but the CFA points out agents have the option to include only the most favorable reviews. Reviews on Zillow are vetted to ensure they are written by legitimate customers of the agents. However, the report points out, the reviews are usually written by customers who have been contacted by agents who request the review. While that means they are not completely unbiased, the report says they tend to be less biased than those on agent sites.

Less reliable, according to the CFA’s research, are the ratings on Zillow and other sites. On a scale of one to five, 80 percent of agents on Zillow and 76 percent on Realtor.com received a five.

Among the more valuable information that consumers can review when choosing an agent, according to the CFA:

• Past sales and current listings that indicate whether someone is a full-time agent and has experience.
• The price range and geographical region of recent sales and which side the agent represented.
• The price history of sales that show how long something took to sell and whether there were price changes.
• Detailed reviews with specific information.

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