What's not disclosed that you would like to see done? I know Atkinson has been pretty forthcoming. On PF, we list what in our reference system we own and what is on loan. Sometimes I might ask a manufacturer to keep an amp say longer because it would be helpful say in my next upcoming speaker review.
For the record, I own lock, stock and barrel everything in my system save for some cables. In the case of cables, it is usually to a reviewer's benefit for them to try different cables with the equipment being reviewed. That said, I've laid out a pretty penny for the cables I do own because some companies are new or small companies that can't afford to have a lot of inventory out in the field for review (that in fact is one of the biggest changes in the industry today and many other industries since the recession eg. Reducing inventory period) or that is not their policy. So if I like it, I must buy the cables.
As far as pricing. Standard is dealer cost is ergo most gear is 50% off MSRP. In fact, in the old days, reviewers got to keep cartridges they had reviewed; not any more. In my 30 years, two companies gave me 40 off and a long time ago got 60 off a cartridge. But that was still when analog was king.
Another thing to take into consideration is that most companies make reviewers sign a contract specifying they will not sell the piece for a year or two. So if something else comes along that one likes better--and in a span of two years that is not jphard to imagine-- the reviewer is stuck. And most reviewers that I know aren't exactly flush with money. Also magazines do no allow reviewers to make a profit on the sale of a review piece. That is ground for dismissal for any magazine I've written for. Nor is a reviewer allowed to barter work say to buy a component. We know the famous story of what happened to a TAS reviewer who reportedly did that.
I'd also add manufacturers like when reviewers buy equipment because of course, they can no longer sell the review gear as new. So it saves them the hassle of selling it themselves.
And for the record, I've never haggled over price with any manufacturer.
That's about as transparent as I think one can get?