Say someone has a complaint against you regarding something they asked you to do. (It wasn't done on time, wasn't done right, took too long, you didn't drop everything else in your life in order to do it for them.) However, you know that their taaneh has no real validity (ex., you're doing them a favor; they're paying you too little to make so many demands; you're already doing more than they could ever expect, etc.) You don't really want to get on the defensive, make excuses or whatever, since the complaint is so baseless. What would you do? Just ignore it? Turn it into a joke? Refuse to work for them/do anything for them in the future? Would you sit down with them and go over the terms and conditions under which you're willing to work with them?

I started to do this but I can't seem to get the tone right. It either comes out overly aggressive or too obsequious and defensive. I think I'll try ignoring instead.

I think you need to be more specific about the situation. Is it work-related? Personal? The situation will partially dictate how you should handle the complaint.

But regardless of that, in my opinion, if you say you're going to do something you should do it well and even if it is a favor or even if they're not paying you enough, that's not an excuse to do a sloppy job, turn it late, etc.

No. The job was not done sloppily, nor was it done late. In fact it far exceeded expectations. The only problem is that this person feels they should be able to expect my full-time dedication and attention to this matter, when in fact I have a life and many other things to attend to. Sometimes in life you need to accept that "you get what you pay for," and if you want something that I am unable to deliver you should find someone else to do it. And if you can't find someone else do do it, then don't come with taanos to the one person who did agree to do it for you.

I find that that sometimes happens in relationships as well. When the other person expects you to overextend yourself and if you can't, they are unhappy.

What's the point of starting a thread like this if you are just going to give a bunch of fuzzy, non specific details that we are left to decipher?
Either post the situation or don't.
No one wants to answer these crappy @ss threads.

Why not just respond to them with the above perception of your truth? Might wake 'em up.

that's not a valid reason. presumably, you knew the terms before accepting the job.

You mean *they* knew the terms. Let's put it this way. If you're paying someone for 2 hours worth of their time, you can't expect them to put in additional hours for free, and especially not to turn their personal life upside down to accommodate you. Maybe, if I have the time and I want to do it, I might put in the extra hours as a favor, but you can't exactly come with complaints if I choose not to.

Crush them...

In a situation as delicate as this, it's very important that you not react the wrong way, while at the same time taking care to do the right thing. Doing more may be too much, while doing less may be constued as too little. I would say that once you've taken all the steps you can, there is no more that you can do. Maybe you can talk to their Rabbi, and see what he can do.
If nothing else, the situation should probably get better as it improves, but it may deteriorate if it gets worse, so be careful. But you have to follow these instructions to the letter if you want it to work.