What about when they say, "I didn't hear you" as their reason/excuse for not following instructions...but you think they must have?
This is a classic! It is either one of two things. Either your child really didn't hear you, or she just lied to try to make the reason she didn't follow instructions look like your fault instead of hers.
If you are constantly hearing this excuse for instructions not being followed, then you should first ask yourself, "Did I make eye contact with my child when I gave the instruction?' If you have a habit of yelling instructions through the house, then you have no way of knowing if the child really did hear you or not. I would have a child come to you first, then give an instruction. This is what I do to make sure I only have to give instructions once, thus more effectively teach my child to follow instructions.
After you have called the child to you, look right at them and say, " I am going to give you an instruction. I need you to go put all the books neatly back on the shelf. OK?" If they know how to follow instructions, then they know they need to look at you, to show they understand the instruction, stay calm, say OK to commit to do the instruction, do the task immediately, and then check back to inform you they have followed your instruction.
So, the answer to your problem could be as easy as making sure your child does the first step to following instructions. If they don't look at you, then they are not really following instructions. Not looking at you, earns an extra chore because it is part of following instructions. I usually don't waste my breath giving an instruction if they don't even do the first step.
It is helpful for some very small children to touch your hand or something to keep them looking at you when they talk to you.
If you gave an instruction, and your child says they didn't hear you, but you are sure they did, then they are being dishonest. In my family dishonesty earns 30 minutes of work time. I automatically corrective teach them for not choosing to communicate honestly, and they do their 30 minutes of work time either right then, or at play time.
Warning! If you really don't know if they heard you or not, then it could be bad to accuse. You don't want to seem unfair to your child. Fairness matters to children. Life isn't fair, but to a child, a parent who doesn't do his research can't be trusted. Your child will feel disconnected from you. This could ruin the Spirit in your home.
I would just make sure you are making eye contact when instructions are given and that they know eye contact is part of following an instruction too.