I don't think a 'welcome pack' is for me, but fair play to you Nathan for thinking of ways to improve your business.
My leaflet pretty much explains everything in bullet points and I talk new customers through payment methods etc.
As for credibility and changing customers' attitudes, I think that comes from yourself, not a welcome pack.
A nice sign written van, logo polo shirt, polite and professional attitude and doing a good job, all helps to improve a customer's perception of window cleaners.
The one thing I ALWAYS do with a new customer is show them how a window dries. I'll start wherever the sun is and by the time i've finished one window, somewhere, will be drying. It may not be totally dry but there will be dry areas. I'll show the custy how clean that 'area' is (and get them to acknowledge the system works) and say to them that all the windows will dry like this.
Not teaching you to 'suck eggs' but I think this the single, most important, thing with new custies. Then I can tell them how I clean in light rain (without going into too much detail).
Another thing I do is:
Offer them FREE deionised water. I say to them 'get yourself a spray bottle' and each time I clean, I will top up your bottle for free, so you can clean your inside windows more effectively and for free. I have quite a few custies who like this. AND it saves me doing them
If I thought about it, I could buy 100 spray bottles (a quid each) and give them to new custies, but I can't be arsed.
Hope that's helpful.