As if washed diesel wasn't enough to watch out for, this happened in Mayo last week:

Quote Originally Posted by The Mayo News
OVER 100 motorists in east Mayo are expected to be left out of pocket to the tune of thousands of euro, after their cars were extensively damaged by ‘petrol stretching’.

The practice of petrol stretching involves adding up to 10 percent of kerosene to petrol, thereby ‘stretching’ or diluting the fuel.
Contaminated fuel has reportedly been sold in recent weeks in the Swinford and Foxford areas, and many motorists who unwittingly put it into their vehilces are now facing repair bills of several thousand euro.
[..]
Though fuel samples have been taken from filling stations in east Mayo, Mr McNulty believes there is no contaminated fuel left.

According to Mr McNulty, Aviva Insurance is the only insurance company that covers fuel contamination under its policies. However, Cllr Annie May Reape has indicated that AXA Insurance may also now be prepared to deal with claims.
[..]
Symptoms of damage to engines due to fuel contamination include loss of engine power; the engine management warning light coming on; engine misfiring; a knocking noise after engine starts up from cold and excessive blow back through the oil dipstick and oil filler cap when the engine is running.
[..]
A retailer who buys in 10,000 litres of petrol, could pay out €15,000 for the fuel, while a competitor illegally adding ten percent kerosene to 9,000 litres of petrol will pay only €14,300, saving €700.
That's a damn small saving for potentially destroying your business and that of your local competitors.

I'll be taking a closer look at my insurance policy.

Which filling station chain do you guys use? Is this happening elsewhere?