Here is my experience with Shadow Shopper.
I was a newbie and had one company recruiting me by email. I got interested and wanted more. Shadow Shopper emailed me. I forgot what they were offering for others but it was free for Bronze Membership. So I signed up. They dangled the shops available only for Silver and Gold members in my face. When they offered it for a ridiculously cheap rate, I bit and became a Gold member. I cancelled before the month was over but by then, I was signed up by a number of Canadian companies. US companies were emailing me as well.
So, though my policy was never to pay to get a shop, I did spend I think $1.99 or $2.99. Had this Forum been around, I would not have any need for Shadow Shopper.
Some schedulers will carry your contact info so you will get new shops as they move around.