I started working for them in 2009 and I've done almost 2,000 shops. I don't think you need to worry about hitting a volume limit - unless maybe it's 2,000. If it's 2,000, I'll let everyone know. I project I will reach 2,000 in about 3 months.
MF does deactivate a lot of people. I think it has a lot more to do with performance than people realize, and, keep in mind THEIR perception of a shopper's performance may well be very different from the shopper's perception of their performance. And, new shoppers sign up every day. Shoppers are a dime a dozen to MF. If they have 50 shoppers in one geographic area, they can weed some out. So if you live in an area with a lot of competition, you may be weeded out faster than if you live in an area of little competition.