Actually, Pascal, that wasn't a trick. It was IMHO an attempted rip-off and Boat/US got caught!
What they actually did was increase the rates before having approval to do so from the insurance commission - they sent out literally thousands of renewal bills with 60% or more premium increases. The commission then said get lost! to their rate request (remember, they billed BEFORE they had approval!), so what Boat/US did to "fix" this (since they were then legally obligated to refund the "excess" premium) was unilaterally go back and reduce values, which, by the way, isn't within the spirit (and perhaps the letter either) of the law. After all, you could look at your physical damage coverage as being $x for each $1,000 of coverage, right? That's how I see it, and I suspect its how you see it too. It's how the insurance commission should see it, but apparently they didn't, because there was no second round of enforcement action.
Gigabite's policy renewed during the time between their change (which, by the way, a month previous they told me WOULD NOT HAPPEN, an intentional lie told to attempt to disadvantage me in shopping for replacement coverage!) and the insurance commission's slapdown. I told Boat/US to get lost and found replacement coverage. A month or so later I was in a West store that I frequent and the manager, who is a friend of mine, told me about what they had done post-commission-review - his sailboat, which was insured with them, had its agreed value unilaterally cut by 40%, while the premium remained the same. Of course that meant he was radically underinsured, and they simply refused to write for any higher agreed value - period.
Beware the secondary effects of this reduction in agreed value, by the way. When you go shop for replacement coverage, if you do, you may find that your insurance record has been "tainted" by this reduction in agreed value, and you find it difficult - or impossible - to get your old agreed value back with a new carrier! When I moved my coverage I was asked for the details of my previous, and I suspect (but can't prove) that there's a database out there that had the details of my policy limits in it which the new underwriter could see. That could get kind of sticky down the road...
It is this sort of practice - which I personally find well beyond outrageous - that led me to drop Boat/US as a company I support after more than 10 years of STAUNCH use of them for my marine insurance needs.
I will never buy marine insurance from Boat/Useless again; I don't do business with people who transact business in this manner.