Tall rooms change the setup before they change the square footage
Two homes with the same ceiling area can have very different labor requirements if one includes vaulted rooms, high foyers or stair transitions. Provide ceiling heights when asking for estimates and clarify whether access equipment is built into the price.
Dust containment deserves the same attention. Skim coating and sanding can spread fine material through open layouts if the work zone is not carefully isolated.
Ask the contractor to separate removal from refinishing
Have each bidder identify the cost and scope for texture removal, repairs, smoothing, primer and final paint. That makes it easier to compare a drywall specialist with a painting company that offers a bundled service.
If the ceiling has an unknown older texture, raise testing before work begins. Material safety questions should be resolved before scraping or sanding, not after debris has already been created.