Over-valued flat

I put my flat on the market in Apr 2014 on the basis of FJL's advice of asking price of 425-450k. THis was even though the previous sales in the block of similar flats in Oct 2013 had been at the 330k level. They justified the price by the lack of decent stock and a huge increase in demand. Despite me being very particular that I was after a quick sale and did not want the price to put people off, they continued to recommend 425-450k. I had quite a number of viewings in the first couple of weeks, but then they dropped off substantially. I then decided to lower the price to 400-425k but this only had a small effect on viewings. After about a month I eventually got an offer at £408k which I accepted, but this fell through within two more weeks. Thereafter I received the odd viewing but no further offers and the agents seemed to lose interest. Ultimately I took the flat off the market completely, In the meantime, two (identical) flats in the block had sold for a price that i would have been happy with - 400k and 429k, one apparently though a different branch of the same agent!