This is quite possibly the most powerful tool in your arsenal of body language tools; the ability to walk away. If the price is too high tell your opponent that while you would love to be able to take the item home the price is simply more than you are willing to pay.
Tell them you are going to have to look for an alternative and ask if they’d be willing to match a lower price if you find it. This will tell you if there is any flexibility in their price and will allow you to return later if you need to.
However, if you do walk away be sure you are willing to lose the opportunity to obtain the item from the seller as the next person they speak to may not be quite as well versed in the art of negotiation and snatch it up at the asking price without a second thought.