Raising the issue of price.

A couple of books I’ve read lately suggest that the real time to make money is when you buy. i.e. it is important to buy at the right price. Part of this means negotiating the deal and here is the bit I need help with. I’m reading that the person who first mentions the price is put at a great disadvantage. Why is this and what do I do when beginning to negotiate to gain the advantage?

Thanks in advance for your help.

Charlie