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.
One thing I know about the rich and poor in terms of purchasing commodity is that the rich have the leverage to buying in bulk, which makes it cheaper in net cost, but the poor buy several of single units because of less available income, which in totality is more expensive. The rich also have the connection to buy from cheaper stores and get it delivered to their doorstep since it is bulk purchase and most of the rich who can afford bulk purchases open retail stores and still make more money from the poor who would buy smaller units. In general, the poor spend more in purchasing commodities.