How to buy a domain that is not available?

How to buy a domain that is not available?

There is a domain I want to buy, estibot has put it $740. Now I have heard these tools are useless, so I paid someone online $5 to give me an "official appraisal" and he said it's worth between $1200 and $2400. I am trying to buy it through Sedo's domain buy service - does anyone have experience doing this kind of thing? And, if so, what do you think I should expect to end up paying for such a domain?

Thanks!