Man, Moondream. I wish I could tell you that yours is an isolated incident. Owners caught neglecting an animals will often become aggressive, turning on the rescuer. When this happens, you have to maintain a professional attitude and calmly inform the person that you have detailed the animal's condition with both photographs and witnesses. Tell them firmly but politely that it is a criminal offense to neglect an animal, and assure them while you are returning the animal to them this time, you will be making report of the incident to the local authorities, who may decide to become involved as well. It usually shuts them up pretty fast, because they know they're in the wrong. If the law gets involved, they can even end up in jail.
Always take photos, loads and loads of them. Have a friendly vet who will assess the situation and will write up the incident. If an animal is severely abused or neglected, do NOT return them. Contact the appropriate legal entities (the police in town, the sheriff in the country) and any animal protection groups immediately so they can help you make the right decision for the animal. Sometimes the vet will house an endangered animal rather than allow the owner to take possession.
If you ever need help, just lemme know! I've been doing this about 2 decades now, so I know the ropes/procedures. Laws vary in all states of course, but Florida is probably pretty similar to TX as we're both purdy rednecky states.