Here's the problem I have with "make an offer":
It's usually one of five scenarios.
a) the seller has no idea of the value and is fishing for a sucker who will offer them $1 million for it
b) the seller doesn't really want to sell it but figures if they get an offer of an outrageous amount they'll take it
c) you make an offer and they use the auction style process as mentioned above
d) the seller says "make an offer" and has an outrageously high price in mind, then is offended when you make a reasonable offer
e) the seller has no idea what it's worth and you make them an offer so they just take it
I hate all of them except option e.