I have declined jobs because I knew I could not deliver results I would want to show. I did an indoor show with the WORST mixed lighting, on top of being a cave. Even shooting raw wouldn't have helped much because it was a mix of florecsent, natural and mercury vapor(OLD building) And, it was dark on top of it.
I was cleared to use a flash and I thought the photos were pretty poor. I guess not, as they asked me to shoot their nationals in 2008. Which, before then I have GOT to go shoot with someone at a dog show. At least I will be showing myself this year.
I would not attempt an indoor show with no flash and a 5.6 lens. You will not get many keepers. Different story if you can use flash