Social proof, or social influence, is used in marketing to shape the behavior of potential customers. Social influence is a trait that many customers display. To sum up: if person X and person Y have bought a product, person Z might also buy this product, because they trust in the decision of persons X and Y. This is classed as social influence, and has an important impact on the decision to buy the product.
The concept of social proof originates in psychology. Many people view the behavior of others as an example of how they should act. They trust those around them and often make the same decisions. They essentially imitate the behavior of others as a strategy to cope with their surroundings. Social Proof therefore isn’t a definition that is only relevant in social media, but it is used in all areas of marketing to systematically influence the decisions of customers. Television advertising and cooperation with prominent figures are based on the concept of social proof.
Social Proof can be seen as a similar concept to that of authority, trust and reputation on the social web: if many users trust a source, for example a website, this is an indication for others that the source is reliable. This website will therefore have a certain authority or reputation.
Techcrunch has identified 5 different types of social proof: 
1.) Expertise: an expert in the subject will recommend a product based on his/her technical knowledge.
2.) Prominence: famous or popular people recommend a product.
3.) Other users: ordinary people such as you and I like a product.
4.) Swarm intelligence: if many users like the same product, it is probably worth having.
5.) Recommendations from friends: either direct recommendations from a friendship group, or indirect recommendations from friends on social media.
Regarding online marketing, social proof provides many opportunities to use social factors in marketing campaigns. If a user searches for a term in a search engine, positive evaluations in the SERPs (so-called Rich Snippets) from others can lead to a certain website appearing in the search results.
Social Hubs, which compile data from different social media, can also have a positive impact on the behavior of other users. The same applies to recommendations, positive feedback and seals of approval, with the difference being that here, an institution serves as the social proof. The principle is the always the same – if other users like something, person Z has a good reason to like the same thing. Social Proof can be easily conveyed – for example, on social media there are buttons that show the number of followers, likes, shares or recommendations. It’s a bit more complicated to integrate this sort of data in Spinnets, which should be shown in the organic search. The relevant structures and format of google would have to be observed here.