Hey mate good luck with a choccy lab, they are rare, but i believe a wonderful dog. ( supply and demand may limit cost)
RSB are not cheap for dogs and they can be knocked back for many reasons, we had one last week that had failed due to eye problems (cataracs SP) a very very well behaved puppy. We have had dogs that have failed due to a hip score, but the rsb are very strict on this and the hip score could only be slightly out. Unfortunately some fail for being thick, but i guess we can all suffer from that. Of course some fail from accidents whilst in training. (umm)
So a bit of everything i guess.
You do get a very well trained dog, with an excellent history that is very willing to learn.
German shepherds suffer the same hip score problem, and some suffer temperment problems but to be honest i don't know what this is like in Aus so I won't guess at it.
At the end of the day, which ever dog you choose usually has it's own personality that fits in with you, thats what makes them so special, so very special.
We are like grand parents with grand children, we get to give them back after a short period of time LOL, that reminds me we have another next week!