Why is it a problem if somebody with whom you exchanged business cards after an IN event calls, sends an email trying to promote their merchandize? I guess there is a reason why even the IN site has a market palce tab.
This is personal but I may be true (Not that I have ever called someone trying to sell them something), I feel it's normal; very okay. Don't make fun of people who are trying to make ends meet. I suggest if you already have what they are selling or uninterested in their stuff then you tell them, no thanks. If they continue calling / sending emails then, I myself would be pissed too.