Old ceilings reward careful substrate diagnosis
Cracked plaster, previous repairs and uneven transitions can become more visible when texture is removed. If the ceiling is not sound, stabilization or repair should happen before the cosmetic finish. Ask the contractor what they see, what is included, and what would trigger a change order.
Where crown molding or detailed trim meets the ceiling, discuss edge finishing as part of the scope rather than assuming it is routine.
A plaster-smooth finish has its own workmanship standard
Ask how many passes or coats the contractor expects, what sanding is required and whether the surface will be primed and painted. If a covering method is proposed, ask about thickness around fixtures and trim.
Unknown older texture should be tested when appropriate before disturbance. Expertise in plaster does not eliminate the need to identify suspect material responsibly.