Once you have sufficiently advanced robots, doesn’t the cost of most goods dramatically reduce since the labor is taken out of the entire supply chain?
Usually, post-scarcity as an element deals with matter replicators/molecular assemblers that can build anything out of raw materials.
See Diamond Age, Accelerando, etc.
Resources are always scarce. Energy and raw materials will always be expensive, and the demand for energy and materials both increases as they become more available (keeping the price high).
Nothing is scarce in space. There is limitless energy in the atom’s nucleus. We just dont have an effective power plant yet.
Maybe nothing is scarce but you should know how, when and where to look for it.
I think the main issue with this argument isn't really whether it's a post scarcity civilization or not, but the implying that any alien civilization, especially an advanced one, would also develop into an almost exclusively capitalistic society like us. It's going way too much into anthropomorphizing territory.