If you have the "nice guy" problem like I did, my rule of thumb is: phrase things in terms of your personal needs. - "I do not have the time to do XYZ, sorry"

If you have the "nice guy" problem like I did, my rule of thumb is: phrase things in terms of your personal needs. - "I do not have the time to do XYZ, sorry" - "It would cost me too much to do XYZ, sorry" - "This framework does not support XYZ, sorry" These are conversation stoppers. As opposed to: - "I think this goes beyond the scope of our agreement" - "What you are asking is very difficult"