As locals in Twickenham, we approached Dexters with regards to the letting of our house. We bought into their sales pitch with promises of a buoyant market, Landlords receiving asking rents and masses of applicants registered - what a mistake! Two weeks into the marketing, we discovered that they were showing applicants with budgets far shy of what they had valued the house at, and after the first week, viewings dried up completely. There was a distinct lack of feedback - we had to chase for this after every viewing; most of the time it was non-descript and we were none the wiser.
The customer service element is dire - you'll speak to a different person every time you get a call or try to call them, and the calibre of their staff is just awful - I later found out from another local agent that Twickenham is the training office for new Dexters staff - this explains everything!
All in all, a dreadful experience, just don't go there!