Can one thinset mortar directly to a painted floor or would we have to rent a concrete scraping tool prior to installing?
There is a risk going over a painted floor and would not be warranted by most thinset companies. Best case is to use MBP (multi-surface bonding primer) to at least enhance to bond of the mortar to the substrate. Do a test area. Still not warranted with MBP. There are shot blast machines that should be able to remove the paint from the surface of the concrete.