@MehdiEG<p>1 - There are two main reasons why listings are kept online even if they are already taken. Firstly, agencies purposely keep listings on so that they can occupy a slightly larger search percentage on property sites. I believe by law they can continue advertising a property for a further two weeks after being taken.<p>The second reason is that when you look at the supply chain of how listings get onto a property site - you can see why listings are often already taken, especially in highly populated areas such as London. An agent has their own website to manage - you can bet they update it with new listings daily but do they remove old listings at the same time? Those listings are then pushed to property portals via the software provider in a feed. Usually it will take at least 24 hours until those listings go live on the property portal, which in many cases may already be too late.<p>2 - In the UK, if you rent through an agency you should expect to pay extra on top. Usually the agency fee covers things like credit/reference checks and prevents time wasters. Imagine if there were no fees and I called up three agencies and told them I wanted to take each property. Then all three removed the listings from their site/property portal - I'm only going to take one property, so two agencies would have their time wasted, maybe all three if I decided I didn't want any of them.<p>Whilst it is annoying for us to call up for a listing that is advertised as available only to find it has already been taken, I think if we look from both sides it becomes more apparent why it happens. In terms of the "extra" costs, it all boils down to data quality. Even if the option was available for agents to indicate their "extra" costs, I can guarantee most would not use it. If they were forced to use it, most would provide inaccurate data.<p>My advice to you, is find a property website that you like searching on. The quality of data (as in the listings) all boils down to the source, the agencies, and nothing can be done about it. The only thing property sites can do is to ensure they keep their site as up to date as possible from the feeds (sometimes low quality) they receive.