As an estate agent for some 25 years, I have to say that I've never heard of this agent, and looking at their website it looks like they only have one property to sell in SW11, two in SW18 and three in SW18, so a pretty poor showing in my opinion. I think that it's fair to say that any agent you speak to will sound pretty promising in conversation (that's their job after all, as ultimately they just want your listing!!), however a better question would be to ask them to send you examples of properties similar to yours that they have actually sold recently, and what the asking price was vs the actual sold prices - I'd bet my bottom dollar that it's a pretty short list.
Depending on where you live I'd be more than happy to give you a steer of what to do next, and what would be your best strategy going forwards. This is not a self promotion, as I am no longer an agent, but generally advise sellers as to how to maximise value from their sale in the shortest possible time. I don't charge for an initial chat, and there is absolutely no obligation for you to use me - it's just straightforward, honest advice.
Feel free to PM me if you would like to speak. By the way, seven viewings in this market is not actually too bad, but if you've not even had a hint of an offer then there is probably much more to it than simply the choice of agent.