4-9k trades over prob 6-8 servers. maybe due to the fact that i had just got hacked that they were paying attention to the account for a limited time?
Nope.
Most likely, you traded your gold with some Chinese company (not being racist or anything!).
If they logged in through chinese IP or a VPN that is known to be used by the chinese gold sellers or they were being monitored by blizzard in any way, your account gets flagged and looked into for trading with them.
At least that's my theory.
So what most people do is, use a Vanilla account just to do the trades.
The vanilla gets banned and the farming accounts keep on going.
BUT sometimes, they dig in enough to relate the vanilla with your account(s) and thus banning all of them in one swift move!
So yeah.. don't get into goldselling unless you're :
a) Trading with someone you know irl/guild (their account won't be flagged, so it will look like a normal trade)
b) Willing to take the risk of losing either the trading account or all accounts with each trade you do.
c) Selling lots of gold so you can cover up your losses if you did get banned.
So in conclusion, there is no "safe" way of selling gold.
You sell gold, you get banned sooner or later, hopefully later.
Good luck!