Well leaving aside Mr I-have-good-feedback-as-a-punter-therefore-I'm-a-legal-expert who clearly isn't the brightest bulb on the Christmas tree, the information you're asking for is basically to save your time being wasted by seeking as concrete proof as is available that the person who has contacted you is going to be at the address they say they are at, and therefore your security buddy will know exactly where you are.

I do very few outcalls as I don't really find the demand for them makes the hassle worth my while, but on the very rare occasion that I do a home visit to a client I haven't met previously (and I would still be checking the name and address on the electoral roll), I've never had any trouble getting the requisite information - most sensible people understand why we're asking and you're maybe just getting a bad run? I find punters who regularly book outcalls at their homes are used to being asked, although plenty don't bother and a look at some of the woeful tales in Warnings is ample demonstration of what usually happens next.

As far as landlines or lack of them go, some ladies will accept a scanned image of a utility or council tax bill with the name and address on - it's not foolproof, but it depends on how much risk you want to take. I'd accept that for a short journey, but nothing outside my home town without a deposit as well to cover travel time and costs (and if somebody is up to no good to the extent that they'll doctor a bill/document to get you to go, you've probably got more to worry about than having the door answered by a little old lady).