I don't think the majority of Locals that you encounter day to day cause any problems at all, most of the people ripped off bought through English Dutch or German estate agents, trying to make a fast buck, there are some good agents out here and all will now be registered and approved whereas 5 years ago it was the wild west!!
The locals don't get ripped off because they know the system and once a property is bought they will never sell again so they are not bothered with Cedulas.
A lot of the builders disappearing after receiving funds for materials again were Dutch English and German, the local builders don't ask for any money up front, but they are usually 3 times the price, again there are builders out here that can be trusted, but they are few

The Lawyers and Notarios transacted property sales up till about 2 years ago without Cedulas, when officially one was needed since 1984, but the law has been resurrected and enforced hear to devastating effect for about the last 2 years

You also can't predict for a corrupt Alcalde giving illegal permissions, that later will be declined by a higher body

The main problem is that Spain joined the EU in 1984 and accepted huge EU grants to improve the infrastructure and provide Electricity and water to everyone, However they spent the money on improving roads.

Now they are up shit creek their solution is to enforce the Cedula and say that no one is allowed to live in the countryside, thus solving the government problem of having to provide services but it has a devastating effect to all who bought in good faith in the Campo and legally!! THEN!!

Lots of people did all the research possible, but you can't plan for retro introduced legislation!!

We didn't leave our brains at the airport as you suggest!!