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.
Do not forget that the rich and poor, and even the middle class are human beings and human beings have different personalities and behaviours regardless of their class. It's time we stop giving every credit to the rich as if they are superbeings, the poor/middle class are not dumb too, only that some factors favour the rich which helps them to be rich.
Taking about expensive and frivolous lifestyles, it's the rich that have it, they do not care about the price of things because they are rich, they just buy. But most poor people will think it twice.