Dog touch aggression

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Hello clicker trainers!

I have a friend that has a 6 year old terrier mix and he is very "aggressive". He has no bite inhibition and bites anyone that touches him or tries to touch him except my friend. And the bites are not just nips they are slashes and deep bites that draw blood. He was harshly handled by her dad (throwing him out the house, yelling, screaming ect.) and I believe he is a sensitive dog. He can be around people and shows no aggression whatsoever. But when you try to touch him that is when the problem arises. They can't take him to the vet because he goes into full blown "rage" as they describe it. How can I use clicker training to help this dog? I know she should see a professional trainer but her father doesn't want to spend the money on the dog because he thinks the dog was just born bad which we all know is not true.