Confirm site requirements
Agree on stand and floor suitability, access behind the tank, safe power placement, ventilation, and practical water-change access. Ask who is responsible for plumbing and electrical work and whether any licensed trade work is needed.
Document the plumbing and gear
Photograph valve positions, fittings, filter models, replacement-part numbers and planned water levels. Have the installer demonstrate normal operation and the safe steps for isolating a leak.
Separate setup from stocking
Water treatment and a functioning filter are not the same as a fully cycled aquarium. Ask what testing will be done before adding fish and who is responsible for follow-up guidance.
Put ongoing maintenance in writing
Confirm cleaning intervals, safe handling of biological media, water-change methods, leak response, and who to contact for a warranty issue. Save manufacturer manuals with the final invoice.