Calling them is usually the best bet - if you are confident on the phone, that goes a long way. Basically just be a bullshit artist.
*names changed* ... /shrug
Blizz: "Good morning, my name is Justin, how can I help you today?"
Me: "Hi Justin, this is Sue, how are you doing?"
Blizz: "Great thanks for asking, and yourself?"
Me: "Yeah I'm doing ok, I'm just calling about the ban that is on my account"
Blizz: "Ok, let me just pull up your account to have a look"
(get account details)
Blizz: "Ok yes, I can see that a ban was placed on your account because of suspicious activity, and the use of a third party program"
Me: "What do you mean third party program? Is this because of Pingzapper? The program I use to lower my ms in game?" *sweet, innocent*
Blizz: "That shouldn't have caused any issue. But tell me, where you doing a lot of herbing in the last few days?"
(there is your hint, he's saying you've been botting for herbs - learn to read them a little)
Me: "Yes I have, in Twilight Highlands actually. I needed the Twilight Jasmine up there for the Draconic Mind pots I was going to make to stock up for Realm First attempts. Figured every little bit will help, you know?"
Blizz: "Ah ok, it looks like you were there for a few hours which has probably flagged your account for botting"
Me: "I'm sorry, botting?"
Blizz: "Yes, where people use a third party program to do things for them, like collecting herbs and ore"
Me: "Oh ok, but no, I was definitely farming by hand. I'm lucky I have an active, chatty guild to keep me entertained on guild chat and vent while I farm for things"
Blizz: "That's understandable. The next time you go farming though, make sure you mix it up a little bit and don't follow the same path all the time, try to not look like a bot to avoid being put under suspicion ok?"
Me: "Will do, thank you for the advice! You tend to learn where the good respawns are and follow that general area, but I'll definitely keep that in mind. Thank you"
Blizz: "You're most welcome. Unfortunately I can't actually unban your account, but if you can submit an in-game ticket, the in game GM's will take a look at it for you"
Me: "Yep, I've put the ticket in, just thought I'd call in to see what had happened as I was a bit lost to the "abuse of the economy" comment in the ban notice"
Blizz: "That's no problem at all. I'll put a note on your account as well so the GM can see what we've talked about and what I've seen on your account as well"
Me: "Thank you very much Justin"
Blizz: "You're most welcome, thank you for being so accommodating"
See? "for being so accommodating" - most people call up & abuse the absolute crap out of them, just be nice, be a little "oh why was I banned?" confused and most of all, be nice! Remember your rep's name, always say, "Thank you *name*" - little things that go a long way.
Good luck with the un-bans guys.

Back from the googlez : Brain Activation When Hearing One Something like that o_- but it gets annoying as hell if people are like "HEY JUSTIN :3" "Him: What?" "So justin why was I banned JUSTEEEEEEEN O_O" "him : *silent facepalm and hangup*