It is a fair question, and the honest answer is that domestic materials are engineered for a dry, still, stable building, and a boat is none of those things. The parts do not fail because they are bad, they fail because they are being used somewhere they were never designed for.
Understanding why is also the clearest explanation of why boat electrics is a specialism rather than an electrician with a shorter ladder.
Domestic twin and earth uses solid or coarse stranded untinned copper. On a boat, salt laden moisture wicks along the strands under the insulation, so the conductor corrodes where you cannot see it. Marine cable is tinned specifically to resist this.
A building does not move. A boat pounds to windward. Solid core cable work hardens and fractures, usually at a terminal, and the resulting intermittent fault is miserable to trace. Marine cable is fine stranded so it flexes rather than breaks, and it is supported at close intervals for the same reason.
Most boat circuits are low voltage DC, where currents for a given power are much higher and voltage drop over a run really matters. Cable sizing on a boat is often set by acceptable voltage drop rather than by current capacity, which is not how domestic sizing is approached.
DC also does not self extinguish an arc the way alternating current does, which is part of why fusing and terminal protection are treated so seriously.
Domestic terminal blocks, choc block, push fit connectors and unsealed crimps all fail in damp, moving conditions. Marine practice is correctly sized crimps in adhesive lined heatshrink, supported cable, joints kept high and dry, and fittings rated for the environment.
Using the right materials costs more per metre and saves a great deal in fault finding, reliability and, occasionally, in avoiding a fire. It is also what a surveyor or a buyer will look for.
We would not, and we do not. Untinned solid core cable corrodes and fractures in a marine environment, often within a couple of seasons.
They may be perfectly competent with mains, but marine DC systems, corrosion, bonding, galvanic issues and cable support are a different discipline, which is why boats are usually best handled by a marine electrician.
On labour alone, yes. The cable is a small fraction of a job, and redoing a failed connection buried behind joinery costs far more than the part ever did.
Tinned marine cable, sealed terminations, correct fusing and full documentation, quoted in writing before we start.