A useful link for economics students relating to consumer behaviour –  https://timesofindia.indiatimes.com/business/international-business/fifth-largest-diamond-in-history-sells-for-40-million/articleshow/63283531.cms
See below where to find the relevant section within the spec:
Edexcel spec reference  1.2.2 The concept of diminishing marginal utility and how this influences the shape of the demand curve 
AQA spec reference Consumer behaviour
OCR spec reference P 7 Explain the relationship between price and quantity demanded using marginal utility theory