Three appliances, one visit
A kitchen with a Sub-Zero in it usually has a second unit in the butler’s pantry and something for wine in the basement or the dining room. They were installed together, they have run the same number of years, and their condensers have collected the same dust. Reading all three while we are in the house costs a fraction of what booking three separate visits costs.
It also catches the fault nobody called about yet. A wine cabinet whose zones are quietly converging, or a pantry unit whose fan has started to run hot, gets found in ten minutes when someone is already there with a thermometer and a clamp meter.