Thanks for the many replies guys. I have actually used that guild inviter I think, and used the option to set a message to whisper people before invite - but I was on a toon that didnt have invite powers - so all it did was spam people, and try invite them but couldnt. Effectively, it was a whisper bot.
But whisper spamming is not only annoying for most (and I doubt people will take you seriously when you interrupt them mid game while they are in action) and plus, it is limited to only X amount of people per Z amount of time. AKA - There is a cap. Once you message a certain amount of people, you need to wait until you can message more. So, for example - you might only be able to send 50 whispers per minute ( to different people ) - and if you tell them something like, that you may have gold to sell, chances are by the time you message the first 50 and wait a minute, you wont be able to message any more after that because people will have reported you and you go on auto lock down until a GM investigates - and we know what happens then!
I have tried it for myself before, just so I knew if it was even a possiblity - but it isnt at all.
Keep the informative replies going!