Vic, Dawn,
You probably aren't going to like what I have to say, but...
I think what you are describing is a "free market." If the mobile home manager has some vacant homes that he is willing to offer for sale to potential buyers, then he will only attract those buyers if he presents a better overall value proposition (better homes, lower costs, or a combination of both) than your mom's property. If he does that, then your mom simply has to compete.
It might not seem fair, especially since the park manager probably is more visibile and has other advantages, but I don't think it is unfair or "unethical", and I give the manager the benefit of the doubt that he isn't being "mean-spirited."
The only recourse your mom might have is if she and the manager signed some type of buyer contract and in it there was some type of "non-competition" agreement with regard to future sales, and the agreement barred the manager from soliciting potential buyers. I've not heard of such things, however.
TJR
