Now, law enforcement and manufacturers are trying to fight back and keep fake products off of local shelves.
But as the I-Team found, counterfeit electronics are very common - and could be hazardous to your health.
ABC7's Chuck Goudie joined law enforcement on a Los Angeles raid, where they targeted businesses that authorities suspect are selling fakes. Investigators say they can be found at discount stores here in Los Angeles, Chicago flea markets, and even internet retailers.
"If there's a legitimate product developed made or manufactured, there's also a counterfeit counterpart, it doesn't matter what it is," said Detective Barrett Halcromb of the Los Angeles Police Department.
Workers at this store claimed not to know these were knock-offs so they were cited and warned to stop selling.
Police say the profit margin on fake goods is so high that gang members have started selling fake electronics instead of drugs.
"These kind of goods, they go to fund you name it, organized crime, terrorism," said Halcromb.
"Counterfeiters actually take the copper out of the wire," said John Drengenberg, Underwriters Laboratories consumer affairs manager.
This is why fake electronics are a big concern.
"It becomes a dangerous product in your home," said Drengenberg.
Underwriters laboratories in Northbrook showed the I-Team just how dangerous products such as counterfeit extension cords can be.
When the UL expert plugged in this normal looking extension cord, it started smoking heavily -- and burned right through the insulation!
"Very often extension cords are under couches, they're near drapery, or curtains - you just don't want this happening in the middle of the night!" said Drengenberg.
ABC7's Goudie asks: "You can tell by how flexible it is, that there's not enough copper in here?"
"Absolutely this is way too flexible for the type of cord that it's advertised to be," Drengenberg said.
Counterfeiters fake all kinds of common electronics, from toasters to holiday lights -- even to fake components in a wall socket.
"If the insulation isn't good, it could start melting inside your wall and that could be a danger, that could be a fire," said Drengenberg.
UL designed a hologram to mark products that their inspectors have certified as safe. Experts say you should check reputations of online sellers, and stay away from good deals at flea markets.
"It's very difficult to determine a counterfeit product, they look exactly like the real thing, but the red flag is: are you getting it too cheap? And if it's too cheap then you should be very concerned," said Drengenberg.
Back in L.A., after tracking the accused distributor of the fake goods, undercover investigators arrested him on charges of selling knock-offs.
Inside his store, investigators found what they say are fake popular "Beats by Dr. Dre" headphones, chargers, and fake Apple iPods that look just like the real thing.
"When our undercover officers went in he said he said, these are from China, these are almost as good as the real ones," said Rick Ishitani, detective supervisor at the L.A.P.D.
Experts are most concerned about counterfeiters faking low-cost high volume items - like extension cords and phone chargers - because they're easier to pass off as fakes.
One suburban flea market has gone so far as to create wanted posters telling customers to be on the lookout for fake goods.
UL Tips to avoid fakes:
More tips to identify counterfeit goods