The answer may vary depending on the type of relationship, so consider this general pointers:
Regarding the inferior motive, if you feel like you are being approached with a dishonest question you can always address this in a respectful manner. More specifically, you avoid being disrespectful if you phrase these things based on your reactions, and not on the other persons behavior.
Furthermore, we can never be entirely certain about the other persons motives, and this way of addressing things leaves the possibility open for others to give their perspective on things. They may have good reasons for acting the way they do, even though it doesn't seem that way at first glance.
The general formula is to describe:
- The situation as objectively as possible
- Your own thoughts/feelings
- A better alternative (if possible)
- End by asking for feedback (if you want it)
A strictly hypothetical example of the formula above could be: "When i am asked for things (1), i feel like i am being taken advantage of (2). If you actually want me to do X, i'd appreciate being asked in a more straight forward matter (3). What's your opinion on this (4)?"
Remember you are in your full right to say no. The exception to saying no - and perhaps considering a compromise - is if you have received several favors from this person in the past.