If you ever visit farmers markets, craft shows, or startup eateries, you have almost certainly noticed an increasing number of vendors accepting credit cards using small devices attached to smartphones and tablets. With names like Square and GoPayment, these devices offer young or small businesses the ability to accept cards with little up-front investment and low transaction fees. Some brands accept only conventional magnetic-strip cards, while others are also able to process modern chip-based cards; others use near-field communications to accept payment from a mobile device held near them (Apple Pay is the most well-known version of this technology).

The growing presence of this payment method prompted reader John Emery of Watertown to ask: Is paying this way safe for consumers?

Emery — and anyone who has ever hit the farmers market low on cash — will be glad to learn that the answer is a pretty solid “Yes,’’ especially when interacting with the established players in the field.

“I would view Square as just as secure as any other payment processor, in terms of security for the consumer using the card,’’ said Danny Rogers, chief executive of Terbium Labs, a Baltimore company that tracks stolen data in cyberspace.

Square and competitor GoPayment, from QuickBooks, both encrypt every transaction and do not allow card numbers, security codes, or magnetic-strip data to be stored on vendor devices. Their software complies with the Payment Card Industry Data Security Standard, a set of requirements designed to improve security and reduce fraud. Internal procedures limit the access employees have to systems and data, as well.

Furthermore, security breaches are much more likely to happen to large, traditional retailers, Rogers said, pointing to the 2013 Target security breach in which the data of as many as 70 million customers were compromised.

“A lot of the brick-and-mortar stores use older systems with more points of vulnerability,’’ he said. Square, on the other hand, uses a “very advanced, modern infrastructure that’s harder to attack.’’

Ironically, though these are safe for consumer use, they are often used by data thieves to convert stolen plastic into ready cash. The criminals set up a business account on a mobile payment service, then use stolen cards to make “purchases,’’ pocketing the proceeds.

If your card is safely in your wallet, however, go ahead and whip it out to buy those fresh local tomatoes at the market.

Have a consumer question or complaint? Reach Sarah Shemkus at seshemkus@gmail.com.