Patrick Villiers is, of course, quite right (Patricks are always right, OK?).
I understand the unwillingness of the present owner to let it out of his hands for inspection. These rifles often lack one or more of the internal parts, such as the magazine spring, the cap on the end of the spring that stops the spring expanding forwards in to the loading mechanism when there is no cartridge left, and the odd lever thingy that separates the cartridges when loading, so that the system does not try to load 2 cartridges. I would not want to lend out a rifle with the risk of having it returned with one of these parts missing or replaced by an inferior example! But for this very reason, you must inspect the rifle thoroughly before purchase.
So a fair way of satisfying the interests of both parties is as follows:
You arrange to meet the seller, taking with you a proper set of screwdrivers that will not ruin the screw slots, plus cleaning rod, patches etc. - and an appropriate amount of cash.
You agree on "This is the price I will pay you, cash, on the spot, no further haggling, if I can remove the action from the stock here, right now, in front of you, clean and inspect the bore and barrel channel, and am satisfied with the result."
If the seller was, for instance, myself, with a good conscience, knowing that all is OK beneath the surface, the response would be something like "OK; but as it is my gun, I'd rather dismantle it myself."
Good idea? - No risks for the seller or buyer (apart from your ability to evaluate what you see!).
Patrick