I do not know how niched sites operates, but unfortunately even some of the most reputable guys just move the guy into a different account and say they shut him down because he's making them sales. I don't think that's the case with Niched Sites, but I've seen it before with others.
BTW, your thread title kinda makes it look like it's Niched Sites who is the spammer, which is almost definitely not the case. maybe try their customer support first next time. Just my 2cents