Sorry Woodbug but it is blinding obvious that the original poster does not pay the taxes which he should, as he exhibits a total ignorance of them.
Sorry, but in passing, from:-
"Besides, nobody asked if the enquirer had a business tax/VAT registered in another country"
It is apparent that you too ether have misread the post or are unaware that a person who runs a business in Spain must pay the taxes and fees for that income here in Spain.
Also, the admittance that the poster was doing illegal taxi runs, either ignoring or blissfully ignorant that he and his passengers had no insurance cover, thus putting all road users at risk, shows that he has not sought any professional advice on running a business or coulod not give a damn.
Although I accept that further putting down those who already down there is not very nice, a person who, almost insultingly to the rest of us, asks how we could help him expand his illegal business, is a bit rich and inviting criticism.