The UserVoice blog makes a good point that you shouldn't keep customers at all costs:
If you wrangle a wrong-fit customer into continuing to use your product, they will cost you in:
- Time you spend answering their emails asking for things you can’t do
- Reputation damage via their public complaints about how your product isn’t satisfying them
- Even more reputation damage when they finally announce they’re moving to a competitor
Instead, they suggest sending wrong-fit customers to the competition, which should bring a number of benefits, such as having them talk about how nice you were to them even though they didn't purchase your product, and perhaps getting them as a customer later, if your product becomes right for them.
It's worth clarifying that in this case we're not talking about toxic customers, who are actively noxious and never desirable, but merely "wrong-fit" customers, who are desirable but simply not right for your business right now.