However, to me, there is a line. "The customer is always right" can't be literal.
I have no issue parting ways, with a full refund, for toxic customers that repeatedly use abusive language with my employees. Especially when it's not relative to the situation. These kind of customers do exist. It's not common, but do e-commerce long enough and you'll run into one.
There are also (not often) customers that engage in return fraud or other activity that is just obvious cause to avoid them in the future.