If they knew they were obliged to disclose it, so if any of the invoices for the work are to them then they did now about it and they have committed an offence under The Consumer Protection from Unfair Trading Regulations May 2008 (CPRs). These incorporate The Sale and Supply of Goods to Consumers Regulations 2002 and contain a general prohibition against unfair commercial practices and, in particular prohibitions against misleading actions, misleading omissions and aggressive commercial practices. The Regulations are enforceable through the civil and criminal courts. The CPRs create an offence of misleading omissions which would not previously have been an offence if the consumer had not asked the right questions. So if a salesman knows a car has, for example, been badly damaged and repaired and does not tell the customer, he could later be held liable if the customer subsequently discovered that the car had been damaged and repaired. This is in addition to subsequent legislation such as the Consumer Rights Act 2015 and previous statutory and case law. More here: www.honestjohn.co.uk/faq/consumer-rights/