Hi there.
I've had a few calls from them myself. They sounded genuine and honest, checked out the web site, all looked ok. thought i'd do a bit more digging on them. Went on the FSA web site as they said the were registered. A company called Pro smart was registerd untill 2006, they were based in rochester, kent.
I then checked out the address, the post code was no good as it was incomplete, luckily 125 old broad steet in a new ish development 2008 and has a web site with a list of current tennants, yes you've gussed it, they're not on the list.
Like the other post, if they're any good they don't need to cold call and if its to good to be true then it isn't.
Andrew