Ok, here goes:
Whenever you see someone in trade saying "Buying ALL Lichbloom/Icethorn/Etc etc in BULK, just send CoD" or any form of something similar with Saronite or anything to the like you need to initiate a conversation with him/her. Start off by just talking to him like normal and eventually get onto the topic of how he goes collecting all the mail he gets from the CoD. What your looking for is someone who uses the "Mailget" addon.
What this addon does is automatically grab all your mail out of the inbox. There is also an option to "Automatically accept Cash on Deliveries", which from my experience is usually checked with these kind of people.
If they have this addon, then jump on an alt and mail him tons of herbs/ores/whatever at a highly overpriced (I usually only do 10g over what it is so he doesn't get all pissy and bitch to a GM after you cleaned him out) but after that you can just sit back and collect the money that he automatically paid for.
Couple of general tips:
Mail him some from multiple characters, a couple for the correct price.
Don't do the same guy over and over with the same alt.
Don't do it from the guy you asked about which addon he uses, then he knows you did it on purpose.
Good luck!