Independent proof that the work you paid for was actually carried out.
£225 fixed · no call-out fee · 7 days, 8am–8pm
Drainage work disappears underground the moment it is finished, which makes it one of the few trades where a customer genuinely cannot check the result. A short survey afterwards, by somebody who did not do the work and is not being paid for it, closes that gap — and a shortfall is far easier to raise in the first week than in the second year.