There is a limit to how ethical one would want them to be if one was calling in a favour. One could not expect much assistance from a jobsworth "mr clean" if trying to get off from a serious charge.
I actually have many police in the family ranging from the wife's (useless) youngest brother who will forever be a constable, right through to her sister's husband who is currently a chief inspector.
All appear to me to be normal guys just doing their job, but we have to understand, for all police their hands are tied and they all have to answer to their superiors
Best to keep ones nose clean and / or not get caught, favours invariably need to be repaid