No, absolutely not.
The beauty of Blys is that you work on your own schedule - and only accept jobs that you want to do. You can simply "Decline" the job requests that doesn't work for you without any penalty.
Please note, however, "Declining" a job and "Abandoning" a job are two different things. When you abandon a job you accepted, your "Reliability Rate" drops, and you may accrue an abandonment fee if you abandon within 24 hours prior to booking start time.