Years ago, I moved out of my home and rented it while we waited for it to sell. We had tenants that thought they experienced mold in the home, and learned a few things from the testing company:
1. Mold exists in the air naturally anywhere. It lives on surfaces outdoors, and gets picked up in the air and blown around. For this reason, a professional will take air samples outside of the residence, as well as inside, to establish that the mold level inside is elevated.
2. Mold cannot always be positively identified on visual inspection (mold and mildew are two separate things, and black mold and mildew can look similar).
3. Most molds are generally harmless, although some can be highly toxic.
4. Professional mold testing is expensive, but will be given more consideration should the matter go to court.
Testing ran about $1,000 in 2008, for both surface and air samples. In the end, what was thought to be "mold" was actually mildew.
Having said all that, the EPA has guidelines here on how to handle various building materials that have been in contact with water. For the most part, carpet that has been wet for more than 24-48 hours should be removed and replaced, and in all cases the padding and subfloor underneath should be dry.