Always always always look at the sellers other items, list view, compleated items.
Copy and paste your desired item discription into sellers compleated listings. Research how much an average the item you want sells for. Also if they welcome "Best Offers" them try your luck based on these figures.
Neve pay too much for an item. You have all the tools at your disposal to reaserch how often the seller lists an item and also how much it sells for.