@adifferenttruth You can charge the PITA clients more money, but even then at some point you have to decide if they are worth it or not. There is nothing wrong with firing a client. I work for an accounting firm and we fire PITA clients who are more trouble than profit. Keeping our good staff is more important than keeping a "rich client". We can replace the clients. It's much harder to find the good employees, and good employees leave if they constantly have to work with PITAs.
Sometimes though, it's not as much as the client is a PITA as it is you just have to find the best way to communicate with the client and set boundaries with them. We have a client that ALL the employees wanted to fire about 2 years ago. The senior partner said no, just raise the bill (his answer to everything). We reassigned this client to a different staff member who took the time to get past the PITA attitude and talk with the client. We now suspect the client has a learning disability and we simply changed how we communicated with him. We let him know, when necessary, if what he was asking for was part of the services agreement or not. If not, we let him know how much the fee would be for that service. He has service contracts with his customers and he gets it. Now, instead of everyone wanting to fire this client, we swap pet pics by text and he tells us fishing and dog stories when he comes in the office to drop off documents.
As for the constant changes, how well do you listen to the clients in the beginning? We have a very lengthly initial consultation with prospective new clients, we ask a LOT of questions, and we listen. Instead of saying "we can offer X, Y, and Z", we now say, "What would you like to see from us? What don't you understand about your biz? How much do you want to be involved?" We're off to a much better start now with our new clients, by obtaining their goals and setting expectations of how we can help them meet those goals. We also don't hesitate to refer prospective clients to other firms if we feel we can't meet their needs (or, in some cases, feel they'll be a major PITA that we won't be able to satisfy no matter what we do, LOL).
Some clients will always be a PITA and those are the ones you ultimately need to fire. Other PITAs just need some patience and firm guidelines to become your best customers.