I think a lot depends on the trade.
I as a DIY guy can sand my floor and paint it with many coats of varnish giving a yacht finish which any pro could just not afford the time to do.
But as we move to the more technical trades the DIY man just can't afford the equipment required.
One of the major problems is keeping abreast of technology and throughout my careerer I have been sent on main courses to keep my skills to the level required.
However many sole traders feel they don't need to attend these courses they have been doing the job for last xx years and don't think anyone who lives their life in a class room can teach them how to do their job.
As an electrician there has not been much choose but other trades for example a plumber can still do work in a domestic without qualifications and when he does get them are normally limited to gas side of things and not so much on the water side.
However as allied trades we do get involved with other trades and we do see some of the problems.
Plastic pipes is one of the major problems. They must have the matching inserts and joints mixing makes can cause them to fail. There must be some slack to allow for expansion and contraction. And often needs retaining washers or rings. But installed correctly it is far safer than copper as it does not transmit electrical faults between rooms.
I have used plastic for air for many years at far higher pressures than water systems and once learnt it is far better.
So for my disaster. New bathroom was to be fitted while my wife was in USA and I was in London by my children. To be fair they did a good job but it seems my daughter went OTT on clearing up and cleared up a small washer. It should have fitted in the recess behind this shower terminal
As a result after a few years the unit leaked and not a great amount so went unnoticed for a long time. Finally the ceiling gave way.
This was an insurance job in fact two insurance jobs as carpets came under contain and rest under building. Now we have the professionals on the job. Holes cut in walls and the leaks all cured. Well that's what I thought. However they also failed to note the washer was missing so same thing happened again. This time however found before the ceiling fell down. I had even commented to the plumber was there not something to hold the pipe in place as every other joint had a screw up system to tighten on the pipe.
It was when I went to replace the outlet that I found on the web site the missing washer. However this was at least another year after the first disaster so didn't even tell the company of the mistake made. Had the ceiling come down a second time then again would have been an insurance job. As to if anyone would have admitted the previous time the washer had been missed. And even if it had proving they had missed it rather than me having played with it and lost it would be hard to prove.
Likely all would be blamed on using plastic pipes. However the professional will not relate to this potential disaster as they are unaware it ever happened.
Yes I have made mistakes but as to being a disaster again likely I would not know. Likely I would have left site and swapped jobs before any of my mistakes would have caused a disaster.
Even with my mothers wet room where the builder left the lintel unsupported at one end, destroyed the under floor heating mat, and used tile cement which would not set. Meaning we had more work to put the job right than if we had done the job from scratch. The builder walked off site and again was unaware of what was found. I would hope LCBC would have hounded him but when we went to see them they had gone. Clearly stopped trading. The electrician never completed his work having temporary removed the RCD while he located the fault. But again likely he never got paid by builders and would be unaware of the state the house had been left in.
I have as an electrician left jobs uncompleted. One I remember was in Liverpool where the job was to have ended on the Wednesday and I had found a new job in Ulster and had booked my flight for that evening.
When I came to commission I found a set of sockets were all faulty. Not fitted by me but clearly needed fixing before the store could open. I was asked to stop and fix but pointed out non-refundable flight fees which they were not willing to reimburse for me so I in turn would not stop and finish the job. I am sure to the guy who wanted to hand over the store in the morning this was a disaster?
But what seems a disaster to the DIY man is probably just a bad day to the professional. Unless it involved claiming of insurance then I would not consider it a disaster.
When I went to work on the Falklands on the building of the airport in 1984 the company had planned for 20 deaths during the contract and took 20 coffins out with them ready. 6 were returned unused. I am sure the family of the guy who fell off the roof in the snow considered it a disaster but to LMA it was within the planned allowance.
