Ok reporting back after two days of testing my theory. It sucks. None of the gold sellers fell for it, every present got returned except one or two which I guess are sat in an inactive farm bot's mail box.
The plus side is I tried one of the other techniques and it had about a 25% success rate, picked up 125g in the hour I was online. Basically I did the same as above, used the same letter, and sent it out to players.
I used the GM name from the most advanced guild on the server, with an accent over the vowel. I did this on both factions.
I then sent out random mails with titles such as "Sword of Zeal" or "Giantstalker Bracers", and CoD'd them for 25g each.
Made sure I put a line in there about them returning them if not so I could AH the item for 200-250g.
What I found helps to up the percentage a tiny bit is slightly ruthless.
Go on to the guild websites for the guilds on your realm. Look for the bad applications (specifically those from people under 16) and use them as targets. By god the kids are gullible.
Another one I'm working on is using the successful applications. You make an alt in the same fashion, GM name with an accent, and then send the successful applicants a gift-wrapped item.
Call it the "Welcome to the Guild" message, and put some crap about a joining fee in return for something all guildies should have...that'll peak their interest and disarm them enough to accept.
Good luck!