Rig shots are not for the squeamish, clumsy or foolhardy. You are risking damaging a car every single time you attach any kind of rig to it so you need to decide if this is a risk you wish to take. You may have, and should have, third party liability insurance but this doesn't make it OK to damage a car. In some cases Insurance cover distinguishes between moving and stationary vehicles so you may not be covered in the event of a mishap with a rig! Vacuum cups can also damage paint surfaces, although it's not common, so are you really going to attach them to a prize winning paint surface with the owner sweating bullets behind you? On the other hand a 'journo' or 'press' car supplied by a manufacturer for a road test can have all manner of indignities thrown at it. After all, that's what they're there for.
If you are not confident in your ability or you simply do not have any understanding, knowledge or experience using rigs or car mounts then you need to consider if they are even something you wish to use as there often other less risky alternatives.
If you attach a rig or boom to an under body then you may risk damaging any suspension components if any of them move or rub on the rig. If you are using vacuum cups on paint/panels then you risk scuffing, scratching, or even denting the paint surface or panel. You may even be risking breaking a windscreen or window if attaching vacuum cups to glass.
You may even accidentally hit a stationary object with the boom or rig, or another car or vehicle might even hit your rig if they don't see it.
Have you taken every precaution that you can? The points below are just a few of the considerations you have to make every time you plan a rig shot.
If the answer to any of
the above questions is a cause for concern then DO NOT PROCEED. The above
is by no means a comprehensive list, it's just food for thought.