Buying the appliance or fixture before checking the ceiling or the board
The induction hob that needs a dedicated circuit your DB cannot spare, the chandelier your gypsum ceiling cannot carry, the dimmer your LED lamps do not support: all cheaper to discover before purchase. A short survey visit or even photos sent ahead prevents owning hardware you cannot install.
Booking tower work without checking permit rules first
Many managed buildings turn contractors away without a work permit or landlord NOC, and some restrict noisy work to weekday hours. The result is a paid visit that ends in the lobby. One message to building management before you pick a slot avoids the wasted call-out.
Treating outdoor electrics like indoor electrics
Indoor-grade junction boxes in flowerbeds, unrated extension cords feeding garden lights and balcony sockets without covers all fail the same way: moisture gets in, the RCD starts tripping, and the search for the wet joint costs more than proper IP-rated fittings would have. Outdoors, specification is the economy.