I had my own part of bad apples in life, with some jobs from the past I truly prefer not to think about anymore. I will write this down only to share how typical good references – from your prior manager or other people you worked with – can become poisoned pills in your new job.
I stopped asking long ago about references, as they are totally irrelevant and there are other simple ways to find out if a candidate for a software development position would be a good fit in your team. Ask him to review first a short 20-lines code sequence, with different mistakes. Then ask him to write his own short code sequence, to implement some standard algorithm. And see how he reacts when he has his code reviewed by you or some other interviewer.
Straight to the point, here are some typical Customer Service related reactions, from both vendors/providers and users/customers, and an analysis of what was good or bad. And how people should actually reply.