Booking one small job at a time
Every visit carries the call-out minimum, so three single-job bookings can cost more than one half-day visit that clears ten jobs. Keep a running list on your phone and book when it reaches three or four items. Vendors also quote batched work more competitively because their travel time is spread across more billable tasks.
Putting a full-motion TV arm into bare plasterboard
An articulating arm multiplies the TV's weight into leverage at a few fixing points, and plastic plugs in gypsum cannot resist it. The mount holds during the demo and fails weeks later. Insist on metal studs, a backing board, or a different wall.
Judging the quote instead of the method
The cheapest quote often prices a different job: silicone over silicone, plugs instead of proper anchors, no anti-tip strap on the wardrobe. When quotes differ widely, ask each vendor how they will do the job. The one who mentions wall type, anchors and cure times without prompting is usually the one worth paying.