I love the phrase, 'Serious offers only' does that mean you furrow your brows and adopt a concerned, sincere persona as you offer 99p for a book worth double?
If you really want the book so bad it hurts then be ready to pay the asking price reagrdless. If it's less important than that then do the reasearch if possible, work on a starting offer of about half the average value but be pleasant about bartering and be ready to stand firm when the price gets too high, just say thanks , too rich for my blood (or something like that) smile and walk away. Nobody's won, nobody's lost and nobody died - all's well.
