I'm going to ask my neighbor to clean up their yard before we put our house on the market
What's the reason behind that?
The mess is giving me stress.
It is good for people to have clean yards and make their house look neat. It is considerate people would care for their properties and help keep the values in the neighborhood up.
I'm going to ask a manager to help me.
Ask your neighbor before you get the manager of the complex. Give your neighbor time to do it, it would be better if the situation was solved through you two first.