@vonlost black listing does occur. I can speak from experience at my school, when an ED applicant broke the contract (and not for affordability reasons), no student of ours gets admitted ED or RD (and we’re a high performing school). Even a legacy who was top of his class was rejected this year. Another triple legacy whose family is a major donor to the institution was rejected. Every student applying from my school gets outright rejected or waitlisted.
And this isn’t just speculation- our guidance counselor has asked the regional rep at Brown that handles our area, and he told her “off-the-record” that Brown takes breaking an ED contract very seriously and that essentially they don’t want to waste admits on our school, since they don’t trust the students to come.