I agree that you need to be prepared to walk. There is always going to be another house that will be what you're looking for.
If it has been on the market for 2 years then it might be that the vendors aren't serious about selling. We have encountered one of them when we were shopping for a flat once and they are annoying time wasters - basically the proprty is only on the market of you are prepared to pay more than a fair price.
Have you looked at lots of properties? If you tell the real-estate agent that you need a reply fairly quickly because you are thinking of making an offer on the house around the corner (even if you're not) it can sometimes bring the vendor to the table a bit faster.