It's all fun and games until they call outside shooter and have 50 people with sniper rifles posted up on the docks.
Lets be real here. If the crims want to play this as a "50 people with snipers" scenario, they'd already be in trouble for failRP. The whole idea here is to invent new and more interesting RP robberies. So if a single criminal thinks he's brilliant and tries to rob the yacht alone, he's screwed. If a small group of 4-5 coordinated crims decide to rob the yacht, they will need a plan other than simply sniping the police force because again, it would be fail RP to snipe the police force before they can even arrive to the scene and create a value of life situation.
Using the argument that crims won't "Play along" is weak because if they don't, they will be admin'd accordingly.
To prevent such an occasion, you could even go so far as to add an itty bitty script that pops text up stating "Warning, this will trigger a robbery RP event, if you do not take this event seriously and enact opportunity for value of life, you will be handled by admins accordingly".
Because the reality is, a real police force would have snipers available, at least one heavy duty weapon to level the boat available and so on. So to force the concept that only criminals can have heavy duty weapons that police don't have access to would be power role playing which is also against the rules.
End of the day, the goal here is to create new and fun interactions. Sure some people will attempt to ruin the fun, but it's no worse than a modder popping on to blow everything up with missiles that the admins generally swiftly remove. We should create something based on a fun idea, then tweak it to prevent abuse. We shouldn't be shooting ideas down just due to potential abuse.