The same symptom can arise from different conditions, and the required part must match the actual model and findings. A description helps plan an enquiry but cannot establish every repair cost remotely.
What the observation tells you
Access, damaged fittings and an earlier repair can also affect the work. A guessed thermostat price may be irrelevant if the issue is a door obstruction or excluded sealed-system fault. Parts availability must be checked rather than promised from the brand alone.
A useful next step
Provide the full model, clear symptom and any written diagnosis. Ask what the quoted visit charge covers and how further work would be agreed before authorising a purchase.
Manuals and supporting guidance
Model-specific instructions take priority. These references support the practical principles discussed here; they do not diagnose your appliance.