Yellow or white spots on the liver usually mean that the rabbit has gotten Tularemia from fleas or ticks and it can be transmitted to man through open wounds.

If you notice the rabbit is lethargic prior to taking it, the animal could have contracted Tularemia or any other number of diseases. After contracting Tularemia, a rabbit will only live a few days, so chances are that if the rabbit was doing its usual rabbity thing, it will be alright.

A general rule of thumb is that lethargic animals or animals that somehow act other than they normally would should be avoided.

Another general rule is that animals which are found dead should not be consumed. I've seen both Les Stroud and Bear Grylls ignore this, so YMMV.