The only time i have EVER received a suspension(it was 72 hours) or ban for giving gold in ANY amount was when i gave my friend 100k, and i was stupid to not have him take it out of the guild bank/give me items. I have never once had a suspension based upon gold given between characters (every 1 of my characters has given or received gold cap to another one of my characters at one point or another). My guild bank currently has 600k and at one point it had over 1.4 million. I have also transferred 5k+ at a time via mail with no problems between my characters...but those are on the same account.

A few safety tips(which i don't even use myself) is to always trade SOMETHING, preferably a blue or green for the gold. Red flags are "given" to transactions when over 15,000 gold for no items at all. All gold transactions through the mail over 10,000 that are not COD are flagged as well.

Having your own guild bank is a very good idea especially if you have as much gold as I do and will in the future. It also bypasses the security features if your guild ranks required to take out gold require an authenticator (post 4.0.1).

I suggest submitting tickets in game and talking to a GM directly about what has been happening, there are means to which your account can be put into an immunity from such flags if those transactions are between accounts registered to your battle.net account. If your accounts are spanned across multiple battle.net accounts you need to inform the GM staff about it so that measures can be taken to prevent this from happening. Ticketing through the site will not get this done as account administration has too much going on day in and day out with all the hacking and BS that goes on.

Hope that helped.