How can we be sure that we aren't? Or rather, how will we ever be able to tell whether we are living in a post-scarcity society, when artificial scarcity is imposed by those with political power?
We don't have true scarcity in housing. What we have is artificial constraints on building being imposed by the state.
We also don't have scarcity in basic foodstuffs. There's plenty of food. What we have is a system of distribution that requires that people exchange money for food, and the only source of money that most people have is to exchange it for their labor. We could instead just give people enough money to pay for basic food, energy and housing.
There is scarcity in other things, and there will always be scarcity in some things, even in "post-scarcity" societies. Capitalist market economies are usually very efficient at allocating such resources, and people would still have the incentive to work so they can get the extra things that they want to have for themselves or their families. Capitalism can co-exist with a post-scarcity society.
A workable but less "morally bankrupt" system would lower the cost of housing by using government policy to increase supply, and would give people enough cash to pay for basic food, energy and housing through a universal basic income.