Hiring the watchman's friend for concealed work
For a visible washer swap, an informal fix is a gamble with small stakes. For anything inside a wall, ceiling or floor, it is a gamble with someone else's apartment: no licence, no insurance and no traceable company means every dirham of consequential damage lands on you. The AED 50–150 saved is the most expensive discount in home maintenance.
Reusing the old pressure relief valve on a new heater
The relief valve is the safety device on a storage heater, and a scaled, ten-year-old valve on a new tank defeats the point of replacing anything. Insist on a new, correctly rated valve piped to a proper discharge point. A technician who proposes reusing the old one is telling you how the rest of the job will go.
Leaving no paper trail on anything involving water
Water-damage disputes in the UAE are decided by documentation: dated photos, licensed contractors' invoices, detection reports, in-app job records. Cash jobs with no receipt leave you unable to prove the work was done competently — or done at all — when an insurer, landlord or downstairs neighbour starts asking questions.