I'm not acquainted with wood foundations as such but anytime wood is near the ground, I would be in constant and periodic watch for termites. Jab the wood with a screwdriver to see if they have ate out the inside of the wood and look for their dirt colored trails/tunnels that they build to crawl in going up the foundation. The south is a well known termite zone and I'd check for them all the time.
Besides the termite inspection, look for dry rot or wet rot. Look for places where water settles when it rains. The place better have drainage that goes directly away from the house cause if any water has settled in the past in a low area around the foundation, then you may have rot. Have an inspection done before buying.