stebrow, the problem is that until you complete 10 shops for Maritz, you are a provisional shopper and you cannot self-assign shops. You can only request them and wait for Maritz schedulers to contact you and assign them to you. All the other shoppers (at least those who have completed 10+ shops) can self-assign. These shoppers are self-assigning the shops immediately when they see them, so they are beating you to the shops.
MF Johnston is correct. Keep applying. Call and ask for the shop when you see it. If they have additional, hard-to-fill shops, you might take them to try to get 10 shops done as quickly as possible. Once you complete 10 shops, it will be significantly easier because you will be able to self assign.