Fixing nuisance trips by fitting a bigger breaker or a less sensitive RCD
Upsizing protection to stop tripping removes the safeguard while leaving the fault. An oversized MCB lets cables run hotter than they are rated for inside walls, and a desensitised RCD stops protecting people from a leaking water heater. Any vendor proposing this as the fix is the wrong vendor.
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.
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.