The one rule that my spouse taught me is to offer minimally 10% less than asking. Her offers always make me question her rationality. But if it's a good deal, hey, why not make it a great deal.
Deciding not to go forward now also means there's a chance the property can sit in the market for a while - and also lead to a better price.
Good luck! As mentioned above, contacting the mortgagor or mortgage broker now also isn't a bad idea. Can get a sense so about financing and when you make offer, you have more certainty about how the financing will go, and that can make your offer more attractive.