A man and his parents must pay £1.6m after selling teeth whitener containing 110 times the legal limit of hydrogen peroxide.
Matthew Hargreaves, 46, and his parents John, 71 and Jean, 72, admitted selling the product and were sentenced in 2016.
An investigation found 30 victims, including one person who needed hospital treatment.
Trading Standards chief Clive Jones, from Powys Council, said the case was a "clear deterrent" to criminals.
The trio, from Knutsford, Cheshire, sold the product at the Royal Welsh Show in Builth Wells, Powys, in 2013.
Powys council's trading standards team launched a three-year, £400,000 investigation into the three after tests on the products at the agricultural showed the hydrogen peroxide levels were "harmful".
Investigators found the three had tried to sell the whitener at about 150 venues, including a shopping centre, as well as online.
The family appeared in Caernarfon Crown Court for a proceeds of crime hearing, which recovers the profits of a crime.
The court heard that the trio owned a number of properties having allegedly made £2.5m from selling the dangerous product.
Hydrogen peroxide is a bleaching agent and can be used to brighten teeth in small amounts, but can lead to enamel and nerve damage if too much is present.
It is legal for anyone to treat themselves with an over-the-counter kit, provided it contains less than 0.1% hydrogen peroxide.
The two men were jailed for 18 months after admitting participating in a fraudulent business, while Mrs Hargreaves admitted engaging in an unfair commercial practice.
She received a six month sentence, suspended for two years.