What Does "Reasonable Offer" mean?

I know that not everyone is swimming in cash. That is fine.
If I know a guy and know that he wants or needs something I have, I'd either give it to him or sell it well below the value because I trust that he plans to use it. To me, that is just what friends do.
NOBODY likes the idea of some assclown trying to grind you down based on some bullshit lie, only to then SELL it somewhere later for a higher price.
That happens way too often.
Now, if I sell something at a price that both I and the buyer felt was fair....then the man lists it for sale later at a higher price, I actually don't mind.
There lies another one....My Dad once told me that the definition of a Good Deal is when both parties feel that they got the better end of the deal.
I read in this thread something sort of similar but rude.....The good deal is where both parties feel a little screwed? Nah, I'm a positive sort of guy so I don't see it that way.