You guard against eroding standards as follows: What does the book say?
1) Is there a 'few frozen drops' on the wings? What does your book say? De-ice, no??
2) Is it 'snowing very, very lightly'? What does your book say? Anti-ice, no??
This issue far, far far outweighs being ripped off. We're professionals, that means abiding by a certain ethic, upholding standards and doing things not only in a safe, but also approved and legal manner.
How do you guard against being ripped off? Simple - when you have applied your safe, approved and legal decision making - i.e. no contamination on the wings, and no precipitation falling - then you tell them that a de-ice is not necessary. If they persist, you call your supervisor over, ask for the resident safety inspector to attend as well and inform your handling agent that you will accept the de-ice under duress and that an official complaint will follow. Record names, times, what was said when and by whom, the lot.
However, have never been asked to de-ice / anti-ice when it was not required, neither in VKO or elsewhere. Have, however, on several occasions had to struggle to get the aircraft de-iced when the crews in their wisdom couldn't be bovverd to heat the rig up for a single departure at oh-christ-hundred in the morning.
As long as the minimum standard of being able to understanding and following the rules to the letter hasn't been met, I cannot take seriously complaints about wiser (or at least more compliant) people overriding your decision-making. Yes, I am absolutely 99.9% sure that departing in the conditions described without de- and anti-icing would have been safe - and thank eff we'll now never find out if that 0.1% chance would have left you with any change.
When you have done it all by the book and they still charge you - then start complaining!