There are hundreds, maybe thousands, of online platforms seeking willing workers, so there are bound to be a few bad apples in that cyber crate.

"They aren't scams in the classic sense, but there are better and worse opportunities," said Kathy Kristof, founder of SideHusl.com, which she describes as the Consumer Reports of the gig economy.

The site has researched, reviewed and rated 250 platforms that take a percentage of income in return for linking people to paying gigs or opportunities to rent or sell their stuff.

The most persistent problems Kristof identified are platforms that exaggerate how much workers can earn or those that require workers to invest significant hours before being paid.

"The bad ones hide their terms and conditions, generally on purpose. Most people click through and agree to them without reading the contract," she said. "It may say the worker has to accumulate wages of, say, $100 before they get paid. Some kick you off the platform before paying you because you didn't follow one of their rules. And on some of them, you can only make a decent wage through tips, which is no guarantee."

Most gig platforms are tech startups. Kristof has seen a number of them go under before paying workers. Unlike employees whose wages are protected in case of bankruptcy, gig workers are independent contractors, with no recourse to recover their pay.

To avoid getting taken, Kristof advises, prospective workers should check out a platform's ranking on SideHusl.com. She also suggests studying the platform's payment formula and researching its reputation.

"Go on GlassDoor, Indeed, Reddit or Yelp and see what workers say when posting reviews and complaints," she said. "When you read a few [reviews] that say, 'They stole my money,' the buyer can beware."

Kevyn Burger