Sometimes “experts” suck. I’ve had 2 projects done to my house that need to be re-done, they were so bad. I would have been better off investing some time into learning to do it myself, which I now have to do anyway.
Having experts do my camper van conversion would be ridiculously expensive. Same for buying pre-made things.
There is a lot to learn about floor, insulation, wiring, charging, cabinetry, water, storage, etc. But learning that is one reason I’m doing it myself. Mistakes still don’t add up to even one piece that pre-fab or shop expert would charge. For example, a galley is about $1200 (sink, fridge cabinet). I built my own for ~$200 and got most of it done in one day.
There are some experts I will trust. I trust one bike shop to do my shock service each year because frankly it’s a messy hassle for me to do it myself, and If I screw up, I buy a new $1000 fork. If they screw up, they buy it.
You didn’t have experts. You had people who convinced you that they were experts.
Same thing happened to me. Their (obvious when it was pointed out to me later) failure cost me a lot of money.