Answers between the lines:
Congratulations on your repair.
I do suspect that both instances of intake valve deposits were probably caused by bad fuel.
Your theory about the fuel tanker being polluted by a previous load is one possibility. Another is that fuel is being intentionally polluted by dilution with some other chemical, probably an agricultural use fuel on which there is less tax. I have read of this happening in Ireland where gasoline/petrol fuel is diluted with agricultural use diesel fuel. I don't know how fuel quality testing is done at the fuel pump in Germany.
They do check in Germany, especially the tax authorities, but nobody wants to even think about getting in trouble with them.
I am somewhat perturbed by your loss of compression pressure though, as I believe this may be caused by a change in camshaft timing. To remove the intake valves and clean them, your garage would have had to remove the cylinder head and camshafts, so there is the possibility of it being assembled wrongly, and this could cause a change in compression pressure, and then also a change in fuel consumption.
I thought so too. Cam timing is thoroughly checked and OK.
When it happened the first time, the dealer repaired it. Maybe the piston rings were gunked up too? I don't know, and they were not taken out during repair.
My service manual only covers my 1.2 engine, so I don't know if the 1.0 has variable valve timing like the 1.2, but I would expect it does.
The 1.oL has shorter stroke but otherwise identical.
As you obviously have the skills to clean your intake valves, you should be able to measure your camshaft timing and verify it is set correctly. Another more remote possibility is a problem with the variable valve timing, but I would have expected the cam and crank position sensors to have detected this.