I did a couple of small jobs for them this year. The first was not paid on time. I emailed the scheduler when I hadn't been paid and was paid immediately. I completed the second job and was paid the same day it was reviewed (so, a couple of days after the job was done).
I don't love that I had to chase down my payment the first time, and the scheduler was very nice and helpful, but he couldn't seem to give me details about the expected payment period for that MSC. I don't mind waiting for payment. If an MSC says they'll pay in 90 days, I might be a little bummed that it's so long, and I might not want to advance a large amount of out of pocket expenses, but if there's a great job that I really want to do, I'll probably take it. But when the company doesn't pay according to any reliable schedule, and payment seems to be made based on when you contact them to follow up on payment, I get nervous. I'm sure if I waited for them to call or email me to submit that report they were expecting, they wouldn't consider me a great shopper. I feel the same way.
Anyway, that was my experience. I'm not crossing them off of my list, but I'm going to be cautious.
Shopper in California's Bay Area