Sure it can happen but you can't look on the negative side. The house has been on the market for two years you say. At this stage it sounds like the vendor would be happy to get the asking price. Also bear in mind he may get a better offer but it can sometimes be more hassle to the seller than a blessing. For instance the new buyer will get another survey done, new solicitors get involved. Generally estate agents and solicitors don't like a client acting like this as it brings alot of extra work to there plate. For example an extra €10,000 might seem like alot of money to the seller but to the estate agent it is minimal as there commission cut would only slightly improve.
To put your mind at ease as for the property to be withdrawn from any websites and that no further viewings take place. Otherwise do what everyone else has to do and that is keep the fingers crossed, sit type and it normally works out for the best.