My Dad was a technical surveyor for a well known window company (a very high mountain!!) and he hated the sales guys. They would go in and promise to do this and that which contravined all building regulations.
Anyway, as for my sales pitch, I go in, look at the job, measure up, and work out a price either there and then if I can or get back to them as soon as possible.
As for an approach, just try to be freindly and addapt to the type of person you are dealing with. If they look like no nonsense people don't waffle on for too long, but if they like to chat, have a chat. If they like you, you stand a better chance of getting the job. If they don't like or trust you, you won't get it even if your quote is low!!
That just how I see it, I might be wrong.
Cheers
Ian