Ask about restraint, because goldfish always look hungry
Ask a sitter whether they can resist your goldfish's begging, because that is the central goldfish-sitting skill. A goldfish will follow a person along the glass and mouth at the surface all day, and every extra feed goes straight through a short digestive system into the water as waste. Ask if they will give only the measured amount you leave, soaked or served exactly as you show them, and take out anything uneaten after a few minutes. Agree in advance that a missed feed is safer than a doubled one. A sitter who laughs and says the fish will get a proper holiday dinner is telling you the water will suffer for it.
Ask about the filter and the water, every single visit
Ask whether the sitter will check your goldfish's filter and water on every visit. Goldfish live in large, well-filtered volumes for a reason: their waste load is heavy, and a filter that stops overnight can let conditions slide faster than in almost any other home tank. The check is simple to describe: water moving, filter humming, surface rippling, and the water looking its usual clarity rather than milky or green-tinged. Ask what they will do if the filter is silent, and agree the first steps, checking the plug and the intake before calling you. Also ask them to note the water level, since evaporation in a big open tank can expose heaters or drop intakes.
Ask whether they can do your water change your way
Ask a goldfish sitter whether they can carry out your water change exactly your way if the trip is long enough to need one. Goldfish tanks often cannot simply coast for two weeks the way a lightly stocked tropical tank can, so demonstrate the full routine before you leave: how much comes out, how the replacement water is treated and matched for temperature, and how the filter media is rinsed only in removed tank water, never under the tap. Ask honestly whether the buckets and lifting are within what they can manage, because a sitter who quietly skips the change is worse than one who tells you beforehand and lets you book a professional visit instead.
Ask what changes they will treat as urgent
Ask what the sitter will treat as urgent in a goldfish. Gasping at the surface, sitting clamped on the bottom, white cloudy water, or a fish that suddenly cannot swim level are all same-day phone calls, not wait-and-see items, because goldfish in failing water deteriorate quickly. Ask if they are willing to send a short video rather than a description, since buoyancy and breathing are far easier to judge on screen. Agree who your backup contact is and which aquatic shop or vet you use, and leave the tank's normal appearance described in writing so the sitter can compare rather than guess.
Ask about space, lids, and helpful extras
Ask a sitter to leave your goldfish's space and setup alone. Well-meaning extras cause classic goldfish problems: a friend added to keep it company, a cute ornament with sharp edges for a clumsy fancy variety, food treats from another fish's tub, or the tank topped up with untreated water. Ask directly whether any of that might happen in their home or yours, and whether children or visitors could feed the fish unsupervised. Once the answers satisfy you, putting the handover in KinsLe with Care Pass lets the sitter follow the goldfish's routine and key details clearly until you are home.