I haven't seen anything posted like this so sorry if it has already been mentioned before.
This requires a lot of initial investment for it to work but the rewards could be multiplied greatly.
A friend of mine the other day had his account hacked and characters transfered off the server. GMs after a week or so got his characters transfered back all and well but it got me thinking. There are still some servers that haven't unlocked the gem vendors (mine being one, unfortunately) and if you were to take a large number of gems over you could make easy profit off of it. Once you have vended off your gems you can take it one step further and purchase a number of items that have higher value on your own server. After that, simply ticket the GM, say your account got hacked, and asked for it to be transfered over, then profit.
The only downsides I can see and I have no answers for are:
a) Does a character being brought back get 'restored' and as such any transactions done cross server are nullfied (ie you come back with same stuff you were xferred off with)
b) You'll need to either make the transactions go super fast (have pre-setup deals or something) or have to claim being on vacation or some such to give the time allowance to do everything.
c) IP logging could screw you over so it would also help if you could get you comp to some connection thats never been used for your account (and probably not a friends so the 'hack' doesn't get linked back to him somehow)
You could simplify the whole process by simply doing the xfers but thats 2 payments both ways, and a 30 day wait on a lvl 70 (in order to xfer up to 10,000 gold). If the server xfers are just charged to your accounts credit card (assuming you're not using a game card) then you might even be able to have that charge refunded thus paying nothing for this.
As I said, its an idea and anyone with more experience with server xferring and such might be able to just make/break the thought. As far as the viability, I know it works cause I know of a few people on our server that have been xferring off, buying gems, xferring back on a lvl 10 and vending them for 2-3x their value, easily.