I have signed as well.
I let out my first flat through an agency and the fee to me was a little over 1 months rent and they tried to flog me loads of crap services.
I assumed that was the fees. I was HORRIFIED when I found out they charged the tenant as well! Really disgusted.
When the year was up, they wanted another set of fees to renew the contract. I said actually I was happy with the tenant (and had researched contracts etc online and checked their T&C) and would do it myself thanks very much. They told me that I would have to pay the full fee anyway as they had introduced him, that year and every year. I said WTF where does it say THAT. They backed down and got the manager who said of course you can do it yourself. The young man had told me a Bald Faced Lie in order to get me to continue with them and get money out of me and I think more out of the tenant as well.
So anyway I told them to fuck off and got an assured shorthold tenancy agreement from smiths and he's been there 4 years and everyone is perfectly happy.
I can see that they got me a good tenant - that was a good service. But charging the tenant? trying to do it every year? All teh hidden costs and hard-sell extras? This industry needs some serious regulation now. And, as you say, an end to charging tenants for things that the landlord has already paid for.