Short sale - Chances of getting it approved?

I put in an offer for $479k on a short sale property. We think it's going to get appraised at $505k or $510. Somewhere between there. Lets say the sellers/current owners are qualified for the short sale. What are the chances that the banks (yes, there are two lenders involved - EMC & CountryWide) will accept this offer? So, we are offering about 8% less then if it gets appraised at $510k. Thanks!