The trainer is a scumbag.
He was more aware of the dog's issues than you were, and did that and now wants to sue you???
If by your user name, you are in Southern California, then I think it would be a good idea to look into how similar cases have been treated in the court system. Dog trainers, and Vets, and groomers are supposedly under a different system when it comes to dog bites, but it may have to do with whether the dog was under that person's control
Get a good lawyer. The rental insurance will most likely pay without a fight, but then they will drop you. And if your dog is deemed dangerous, you may be required to gcarry insuarance. So, you might want to consider using a muzzle on this dog, regardless of the outcome of this mess.
Lots of men want nothing to do with the breed. Other men seem to think all dogs love them and they know better than the girl holding the lead. Some might do exactly what this guy did. A muzzle will prevent anyone else from getting hurt, and in a pinch you can pull that bad baby off in a heart beat.
I would think you might be ok in this situation. But another guy, another day... I think a basket muzzle, at least when you are not working in class, can protect your dog.
Jenna, RN CGC & Babs, CD RA CGC HIC
Heidi, RA CGC
SG3 Odessa, SchH1, Kkl1, AD
Ninja, RN CGC & Milla, RN CGC
Joy, Star Puppy, RN CGC
Dolly CGC & Bear CGC