What were the signs that the prosperity of the 1920s was superficial or misleading

Most of the signs of prosperity that were misleading involved credit. There were so many consumer goods that had never been around before, and people bought a lot of them with credit, meaning they did not actually have the money. "Buying on the Margin" was the main cause of all this and led to the Great Depression. Before the stock market crash in 1929, around 90% of stocks people owned were bought with borrowed money. In short, people used way too much credit, meaning they had a lot of items signifying wealth, but they did not have the money to pay back banks, stock brokers, etc ... much like modern day credit cards.