Was our dog mistreated during a neuter?

The question

Our dog was neutered and within a week had an infection, an abscess, and a hematoma resulting in the complete removal of his scrotum. The vet is claiming it was not a fault on their end however we are feeling as though it was, and are not sure if we should be financially liable for the cost of correction that might have been caused by something they might have done on their end.