I think it is important to make a distinction between trader and consumer in order to establish a balance between consumer protection and ownership rights.
The Sales of Good Act (SoGA) 1979 makes clear distinction [1], requiring that traders ensure 'satisfactory quality' and 'fitness for a particular purpose' in goods for sale [2]. This is crucial for consumer protection, ensuring that consumers are not disadvantaged and receive goods unfit for use. I believe it is not an overly arduous ask, since traders have the specific knowledge in that domain and can inspect the goods for quality before sale. In most cases, traders obtain brand new goods from suppliers and can reject defective goods, thus they do not experience any loss if they practice due diligence. In the minority of cases where traders deal with used good, e.g. used car sales, traders have the expertise to inspect for damages before purchasing and subsequently reselling.
However, the situation is vastly different between two non-trading individuals. These individuals are likely to be transacting used goods and are unlikely to possess specific knowledge to thoroughly inspect the goods during the transaction. Imposing too many requirements may infringe on the ownership rights of an individual. In Marckx v Belgium, the European Court of Human Rights interpreted Article 1 of Protocol 1 of the European Convention on Human Rights (ECHR) to include the right to "dispose of one's property" [3]. Imposing too many restrictions may result in an individual not having a practical means to sell his property. Hence, I agree with Monaghan's view that there exists a "strong argument in favour of caveat emptor" between two non-trading individuals.
In order to impose caveat venditor on traders and caveat emptor on individuals, it is neccessary to distinguish them in law.
[1] Chris Monaghan, 'The Status of the Seller in the Age of eBay' (2011) 20(2) Information & Communications Technology Law 103, pp. 108
[2] The Sales of Good Act (SoGA) 1979, s 14(2) and s 14(3)
[3] Marckx v Belgium (1979) 2 EHRR 14, para. 63
[1] Chris Monaghan, 'The Status of the Seller in the Age of eBay' (2011) 20(2) Information & Communications Technology Law 103, pp. 111