This community is more sadistic than I expected. Not that I'm saying I support the buyer or the original owner for taking such a deal, but intentionally going out of your way to cheat someone of $4500 is far more shady. You don't even win anything by doing this - you piss off some rich kid and struggle yourself with new costs and extensive server downtime to rebuild everything. The only winner is a lucky half-assed server owner who is now $4500 richer for the 2.5 years of work you put into his project. Congratulations.
I do think it's good for you to start a new server and take the players with you (the ones that wish to come anyway). Protect their account info while you're at it or at least make sure they know that it's compromised and no longer trustworthy. But sabotaging things on your way out is just as pathetic as trying to buy your way to a tiny internet kingdom. I don't mean to put myself on a pedestal of righteousness here, but I'm disappointed to find that nobody else seems to think that there's something wrong here.
I agree with you to an extend, though I think we are merely here to "watch" what happen next and the commander is the OP only. No one here has the power to change anything other than the OP.
From the OP's post it tells us that he has already decided to do this and that, no one can stop him. There has to be victim to this case no matter what. Either it's the buyer, the seller, the OP or the players.
I think the OP is trying to protect "his work". He is willing to toss his savings for the server and the player shows he is determined.
What he does is right or wrong is again like I always say, the reader will decide.
If you ask me. I say this is not about trying to cheat a rich kid $4500, if it's that easy to "cheat" then there's no poor people. This is about:
1) server owner fails to secure a deal (talking about a gm can stop him from taking the money safely)
2) buyer fails to see what he is buying (talking about he is willing to pay for something that someone has a copy ...)
Note that the OP does not intend to cheat the buyer's money. Keep in mind the OP will not get any of that. He is unhappy with the server owner yet the server owner fails to remove him from the server before selling. The end result? We see this topic here.
The server owner might not be the winner in the end, if the buyer didn't get what he was "promised" to get, a chargeback might be possible. Then the "winner" will become the biggest loser.
The result I think that will have less damage is that the buyer sees all this and decide to halt the deal. So no one gets hurt, server stays up and running. The OP might get kick out from the gm team but that's what happen in history whenever a rebellion fails. Then according to history the kingdom will struggle to stay because the one that cares is no longer there.
It's an interesting case with unlimited possibilities.