Poor buying when things expensive they are expert buying top in everything and FOMO in also the middle class are expert on buying highest prices and not just buying they buy it with credit.
Rich buys when something is with good price low price poor buys just to spend money.
Middle class behave like poor too they buying expensive.
If I gets what you are saying you mean the rich buy goods even when it costs in the market, while the poor do purchases their goods when it's low in the market. But in the general terms the rich doesn't know if the market is selling at a higher rate or lower rate, they just get what they want at a given prices anytime they need it, they don't consider the price of a goods or what the market is selling at that particular period, in the other hands the poor can gets goods at a lower rate and sell at high prices when stocked for a particular period. That is when the prices of goods becomes higher in the market.