On my calendar, I will put ??? shop fee MSC ??? so that I know I may have something. If other shops come up for the same day or time that I self assign, they get priority.
My only problem with Sentry has been the very, very long wait to get paid. Just got paid today for a job I did in early February. I've got them in the "maybe if I can't find another job and I'm really bored" section of my MSC links.