Before you fire those “can’t please” customers... check a few internal things first.
Many business blogs encourage service providers to “fire” customers that either don't fit their business mode or are abusive to their team. You just can’t please everyone all the time, and the particularly difficult clients can often cost more in emotional turmoil, employee burnout, and profitability. Firing a client is often a cathartic action and allows a manager to demonstrate to their team that they put their well-being ahead of the older, traditional “put the customer first” mentality. However... before you jump to pull the eject lever on the business relationship, stop for a moment as you may have a really good learning opportunity.
is the discomfort that your team is experiencing with this client completely due to the customer? Did the client really engage your company with the goal if being difficult? Or did they come in with expectations which they feel you didn’t meet?
if the customer’s expectations are not reasonable, shouldn’t your firm have determined and explicitly agreed upon them up front before starting any work? Firing the client BEFORE you upset them may be the way more productive move here.
is the customer's behavior bringing out bad behavior in your own team? Can you practice on this customer and see if you can still take the "high road" and not let their antics cause your people to stoop to the same level?
did things start ok and then decline? If so, your client may not be as “toxic” as you believe. They may have been a bit unreasonable and then your lack of noticing the warning signs and continuing to “try” to please them could have amplified and otherwise magnified their reaction into something more unmanageable.
did they complain, you tried to fix things, and then they complained even more? This happens a lot with service providers, often without a clear “if we do _______, will that resolve your frustration?” formal agreement. This often requires WAY more detail than most businesses require. They spend the remainder of the declining relationship trying to work down a punch-list of incomplete items in a futile and never-ending cycle.
It's true that some customers just can't be pleased. Before you jump to pull the "you're fired" lever, make sure you're using the situation to verify that it's truly them, test boundary setting, and learn about what may have triggered the bad behavior. Some people are just bad eggs, but others become bad because of a problematic interaction that then gets fueled by a poor business response.
Learn from your bad customers, they're giving you either very expensive or very inexpensive advice, depending on what you do with the information.