Personally I don't count extras as a contributing factor to the price.
Unless there useful things like extra filtration or expensive accesories. But bits like rock wood and nets have no real value. If your honest you still would bid on the same item to the same price even if it came with decor!!
All sorted - seller accepted a lower offer and hopefully we're both happy and no neg feedback anywhere! Thanks for your input guys, wouldn't have sorted this out so well without you!