Business relationships are all about trust. If you do not have the trust of the other party, it is time you walk away from the relationship. 

It does not mean that you cannot rekindle the relationship.   A client many years ago was becoming demanding and impossible to please. The asked for a quote on a job. I provided a fair quote for the work. They asked me to discount the fee by half. I declined to reduce the fee.  My reasons being that to do so would imply that my first quote was not fair; thereby reaffirming the client's erroneous view that I was overcharging in the first place. Secondly, I was prepared to walk away and have them deal with a competitor who in my view would not value them as I did and would not give them the high level of service they had been used to but were not appreciating.  

A few years later the client called me and asked if I would do work for them again. I said yes.  At the time their daughter was 9.  I attended the daughter's wedding and the family tea ceremony 20 years later and the client and now the daughter are clients.

Walking away can be a reaffirming exercise not the end of a relationship. 

As a Human Reosurces consultant specialising in Industrial Relations, it is often difficult to get clients to accepty that they must obey their legal obligations, even though their competitors are using foreign labour and absolutley snubbing payments that are set down as modern awards. This where you must be authentic and ethical. Most times this workds, other times you cannot help them.

You should know when things aren't going right, listen to your clients, manage expectations. When they are way out, you should know or your not paying attention. 

Great question.  The old Maister trust equation works really well to "test" how good the relationship is and whether you are about to lose a client.   That equation says that the extent to which someone trust you is a function of your Credibility (do you know your stuff, is your product great) + Reliability (do you do what you say you will do) + Intimacy (the extent to which you show that you genuinely care about the person with whom you are dealing), and divide the total by the extent to which you are Self Oriented) (come across as focussed on your own needs, only there when there is a work opportunity, and talk about yourself and your offering).  If you have a competitor who scores higher than you on this then there is a great chance your client is about to walk - and probably wont tell you until it is too late.

You do feel it in your gut when things aren't feeling right. It's all about trust - and as the saying goes 'Trust Your Gut Feeling'. As hard as it is to end a relationship it is  best done sooner rather than later so things don't turn sour down the road. I like your story @Steven Brown about connecting with a client some 20 years later. Thanks for contributing @Greg Reiffel @Michael Simonetti @Keith Dugdale .