I will not point out anyone publicly but i would like to warn people to really do some research on people selling links here on PAL more recently. It came to my attention someone was trying to sell links from one of my sites - in fact 2-3 people pmed me to ask me about this. After a test myself indeed this was the case and i have never given permission for anyone to work as a link broker for my sites.
With that in mind I just think everyone needs to be extra careful - I would recommend not ever PAYING upfront for any advertising unless you trust the person or know them 100% to be legit. I would also advise not to deal with anyone who sells links from Gmail/Yahoo/Hotmail or any free emailing program - you just cannot trust them.
I know from now on my first question will be - do you own the site? - if they don't the conversation is finished. There are way to many link brokers scamming webmasters on the forums and I am sick of it.