Here you need to look at that part of German consumer legislation (and the civil code separately, if they complement each other), which describes the concept of a defect in a product (all possible legal definitions of these states of a product), as well as determining the quality of a product (or otherwise - the purpose of the purchase ) by the consumer.
If the consumer did not determine the purpose of the purchase (quality criteria) of the goods in a legally significant (binding counterparty) form when purchasing, the consumer can further (after the purchase) refer only to how the market sees, in general, the typical purposes of using such goods and the nature of use buyer. And this already imposes on the consumer the burden of proving his innocence in a legal dispute with a counterparty - a seller or a manufacturer.
Let me remind you once again that the quality of the goods at the time of purchase is always determined by only one person in the transaction - the buyer. The one who pays the money. No declarations by the seller, manufacturer or anyone else from this chain of sale of the goods that the goods are "quality" have any legal value until the consumer / buyer legally significantly determines the quality criteria (personal goals for purchasing the goods) or agrees with statements of the counterparty (that the goods are "quality") under the contract for the sale of goods.
Most consumers on the planet fall for the bait of marketers and false claims about the product, without checking, carefully, the quality (they personally mean as the norm) when buying a product. And then, after the purchase, it is too late. Because if the objectives of the purchase (quality criteria) are not specified by the buyer at the time of purchase, then either the federal minimum standards for this type of product or what the market generally considers "quality" or as the court decides come into effect.
Never be lazy, at the time of purchase, under video recording or in a paper, legally significant form, convey to the seller (or manufacturer) the purpose of purchasing the goods (quality criteria). Thus, the buyer fixes not some vague marketing promises (often made as vaguely as possible, or even in brazen false statements - for example, in the USA the FTC is now putting pressure on 700 companies with false marketing, at least creating the appearance of some kind of useful activity for society - wsj.com/articles/what-marketers-need-to-know-about-the-ftcs-updated-guidelines-on-health-claims-11673021785), but the specific formalized requirements for the instance of the product that the seller hands over to it.
Therefore, the process of buying any product that is quite expensive (for the buyer) must necessarily include the stage of formalizing the quality criteria (purchase objectives) of the product. And this is not an easy task.
Conscientiously made reviews of goods (the most formalized, according to key quality criteria and comprehensive - which is what review authors should always strive for) are precisely designed to help save too naive and poorly educated consumers from false delusions that are skillfully imposed on them by cunning marketers of manufacturers (and sellers) and understand what minimum formalized requirements should be put forward for the product at the time of purchase, thereby preparing a reliable basis in a dispute with the seller or manufacturer, if the quality of the product does not meet these quality criteria (purchase goals).