Cinders,
Excellent comment, thank you. You've gone above an beyond.
You raise a very good point here in Oz, re: the small and expensive market. We pay way too much and I'm really envious of the Yanks and their large and very competitive market. Also, the approach of many collectors on here, they are sticklers for value in their sales, which is a good thing. We seem to be bound by 'take it or leave it, there's little choice otherwise...' attitude.
The difficulty in serious inspection is distance. I've handled one of the rifles and feel comfortable knowing a little about its feel, look and maintenance. I used the borescope and got a good feel for the quality of the barrel and it's life (much better than my No 1 Mk III*s) and pulled out the head space gauges to see how it fared, but am only going to be able to handle one other. The final one is too far away and the owner seems knowledgeable enough, but they have a vested interest in selling the rifle, so 'salesmanship' tends to cloud critical judgement from years on the range with the rifle.
I'm probably competent enough to be able to manage most initial mechanical inspections without a gunsmith. Not suggesting I know all they do, not implying I have all the details ready for a methodical inspection. But certainly feel confident to go looking for the main wear points and assess the overall condition, maintenance and originality of the rifle.
As for the holes in paper down range, well, therein lies the largest and most uncontrollable variable - the firer! I won't be putting my hand up for the next Queens Shoot.
Its interesting how many are on the market at the moment because they've sat in the safe for '... many years...' untouched. I suppose the real rifles are not as attractive as plastic and high powered optics? (OK, that probably wasn't called for and those whom raised to the bait, stand down! Just levity, folks...)
Your comments on assessing from the East coast are thought provoking, as I've bought two from the West. How do you go about narrowing down the variability in what the seller is trying to have you accept, without being able to hold it? Photos are certainly the essential component, so how do you get past the usual "...Oh, it's god a good shiny barrel, mate..." when you know full well that it's the dark areas of the grooves that you want to know about, not the immediate bearing surfaces of the lands which should be polished if working properly? Few punters are equipped with a borescope, so they're not in a position to send you down bore piccies...
All good information, and I think your final comment is one that sits well with me. I'll take my time and talk to each of the vendors patiently and see how much they want me to buy their rifles. I doubt any of the three would be a dud.