So your saying that while we had only one Frank 'Forty Gafs' Fahy, the Spanish have hundreds, thousands....???
Well, that would go along way to explain the zoning & construction decisions in Spain.
In an nutshell.
I live next door in Portugal and under the counter payments are part and parcel of the property business.
Even mortgage application forms from reputable banks have/had* questions like:
"1. Purchase Price of the Property:_______________
2. Declared Purchase Price of the Property:____________"
The value to be filled in for Question 2 being inferior to that for Question 1.
Banks, estate agents, notaries, vendors and buyers all in on the scheme. Banks will (or used to) provide part of the loan in cash in brown envelopes. Transactions like this done outside of normal opening hours. There's customer service for you.
* I say "have/had" as they always used to, but I haven't been through the process for a while so not sure what story is right now.
Spanish people I know have told me of similar practises, so I don't suppose it's much different.