Here's what I think -
Seller REALLY would prefer cash. If he takes a trade he doesn't want - he's going to have to turn around and sell it or trade it. Yet another transaction and yet more time spent trying to recoup his original value. What a hassle!
To me it just means they really want the cash and don't want to have to deal with something they don't want to keep.
That's the way I see it.
Just say no.