Thanks for posting!
You're right that this is a Principle Support question. That means the correct answer should pretty explicitly link the premise and the conclusion. In this case the core looks like this:
P: many prospective buyers assume large appliances will be included --> C: sellers who are keeping these appliances are morally obligated to remove them before showing the home or let buyers know they're not included
So we know the right answer needs to link these two ideas; it needs to tell us that if you have this premise, you should arrive at this conclusion.
That's why (A) is a winner. It gives us our premise -- buyers might assume that large appliances are included -- and then gets us to part of our conclusion, namely, that sellers are morally obligated to indicate that the items aren't included.
(B) is incorrect because the argument has nothing to do with whether people mistakenly believe large appliances to be permanent fixtures. The issue is whether the appliances will be included in the purchase, not whether they are built-in pieces of the house.
(C) is incorrect because the argument never says homeowners are obliged to include anything; it says they are obliged to let buyers know about the things they won't include.
(D) is incorrect for the reason you suggested: the argument never suggests that homeowners are intentionally misleading anybody.
(E) is tempting, but according to the argument, they can remove the item, they just need to let the buyers know this.
Does that answer your question?
#officialexplanation