You can earn extra cash by participating in market research or even serving as an online juror. By Cameron Huddleston, Former Online Editor May 13, 2014 Perhaps you've been told -- maybe more than once -- to keep your opinions to yourself. But you can actually make money by sharing your opinions.Marketing research firms are hired by businesses and other groups to get inside the heads of consumers to gauge their attitudes about particular products and services. To do so, they need people to participate in surveys and focus groups -- and will pay participants with cash, gift cards or merchandise for their time. Attorneys also pay people to review cases and offer feedback before they go to trial. SEE ALSO: 25 Ways to Earn Extra Cash You won't get rich participating in market research or serving on a mock jury, but it's a relatively easy way to earn extra cash to, say, pay for birthday gifts, fill up the gas tank or start a vacation fund. Scams do exist, but there are several legitimate opportunities that never ask for payments from participants (a red flag for fraud) and don't share your personal information with third parties -- so you don't have to worry about being bombarded with marketing pitches. Here are some opportunities to consider: Participate in focus groups. Marketing research firms use focus groups to gain insight into consumer attitudes. Typically, six to ten participants are led in a discussion by a trained moderator for one to two hours, according to the Marketing Research Association. Participants are screened beforehand to make sure they are part of the relevant target market for the study. You can sign up with marketing research firms usually by filling out short surveys online and will be notified if you fit the profile to participate in a focus group. Advertisement For example, Focus Pointe Global has facilities in 16 cities and pays between $45 and $250 for focus group participation. To participate in its studies, you must join online by taking a screening survey to find out what products, services and brands with which you are familiar. Then you'll be interviewed by phone to verify your answers and chosen to participate based on whether you fit the profile needed for research. Focus Pointe Global keeps all the personal information you provide confidential, and its marketing research never involves sales or promotions. To find marketing research firms near you, use the GreenBook Directory. It's a guide for companies looking for marketing research suppliers, but it's also a good way for participants to find legitimate firms in their state and visit their web sites to see if they're recruiting. Take online surveys. If you don't have the time or desire to participate in in-person focus groups, or you don't live near firms that are conducting studies, you can participate in online surveys instead. However, you won't be paid as much because online surveys typically take less time. Some reward participants with gift cards or merchandise instead of cash. For example, The Harris Poll, one of the longest running surveys that measures public opinion, awards 50 to 150 points for the completion of an online survey, which can take five to 25 minutes to complete. Survey takers can redeem points for gift cards from retailers such as Amazon and Starbucks, says Larry Shannon-Missal, a spokesperson for Nielsen, which owns Harris Interactive. You would need 800 points for a $5 Starbucks gift card, he says. Be an online juror. Some attorneys use large panels of online mock jurors to get feedback on their cases before they go to trial. However, the jurors must live in the county or federal district where the case will be tried. You can sign up at a couple of sites and receive e-mail notifications if a case is posted in your county. Cases can take 20 minutes to an hour to review. EJury.com pays $5 to $10 per case via the online payment system PayPal. You can't be an attorney, paralegal or legal assistant -- or even related to an attorney -- to participate. EJury says you're likely to have better luck getting picked if you live in a large metropolitan area, where more cases are tried, rather than a small rural area. At OnlineVerdict.com, fees range from $20 to $60, and payment is made by check. You must be a U.S. citizen to participate.