I have always worked along the lines of if something sounds too good to be true, then it probably is. How long have the articles been that you have written for them? And how long did they take you to write? Did you find that you had to put a lot of research into it in order to get them accepted? How would they make enough money from your article to be able to afford to pay $100 per accepted one?
This sounds like a dream job for me, because I am a good writer, and I would love to be able to have a website that I could write for that would reward me for being a good writer, but I would like it if you could give me a little bit more information first, because then I'd be able to make a better decision about whether I choose to sign up or not. I don't want to sign up and then waste a lot of time writing something that I never get paid for in the end.