Twelve traders are being investigated by Trading Standards for selling fake goods on an online auction website.
Five of the traders, all based in and around Stoke-on-Trent in Staffordshire, are large enterprises and could face prosecution, officers said.
The traders were identified as selling suspicious items on ebay and test purchases were made, a spokesman added.
The 12 goods purchased included "designer" clothing, perfume and electrical goods.
Two traders have received formal cautions, one has received a warning and four others have been referred to Staffordshire County Council trading standards officers as they are outside the city's jurisdiction.
Martyn Brindley, from Stoke-on-Trent City Council, said: "For the average consumer looking to purchase goods online, it is extremely difficult to judge whether an item is a fake or not as you don't actually see it.
"Consumers should be aware of who they are buying goods from, especially when they are handing over their personal details.
"They should take the time to study the feedback rating of sellers before they buy."