So...let's take it as read for a moment that the props are real and that the evaluators (and a small percentage of others) are aware of details or information that prove this to be true. They are, however, unable to reveal this information to the bidding public, to the almost certain detriment of the auction.
Why? What possible facts about a public auction could be that sensitive?
I'm not making any judgement here, just a statement of possibilities. I don't know the actual reasons here.
The auction and art world thrives on secrecy. Selling price, asking price, who's selling, who's buying, all of that information can be leveraged to change the market price of items, either up or down. The "insider knowledge" that people like me use to broker, buy, and sell, gives us an edge, and allow us to make profit where another person might not. If everyone knows that the buyer is a tech billionaire with a passion for Star Trek, you can bet that, somehow, that lot will sell for a lot more then if they were anonymous.
Now, as to why an auction house wouldn't write a good, informative, and helpful description? To be generous, laziness. (There are a lot of other, far less generous reasons, as well!) I can absolutely make a case for some items that doing a lot of research, getting scientific analysis done, consulting professionals, etc... is just not worth the cost. This is not one of those cases. There is no reason to spend $10k to authenticate something worth $20k. The profit margin isn't there. In this case, though, if the offered evidence was undeniably solid, I'd have expected the phaser to sell for far more then a mid-grade. In which case, I'd like to think that they'd have put forth a little more effort.
Here's the thing, though. Maybe they are lazy, maybe they think they're reputation is good enough that they don't need to go to such lengths, maybe the cost vs. return wasn't there for them, maybe the provenance is weak... or maybe they just don't care. Once the contract is signed, the items photographed and cataloged, it's up to the buyers to decide if the description is good enough for them to bid. Why put more effort forth then you need to?
There are probably a few dozen fans who could have afforded to buy it. Most would take a look, form their opinion, and bid or pass. Some would consult with others, or enlist a professional to do the legwork and form an opinion of authenticity. From the auction house's point of view, why cater to the masses, the forums, and the entirety of the internet? They're not the ones bidding, and frankly, no matter how good of a job you do, the internet will hate it anyway, so why bother?
That's my generous take. I'm not saying that's what happened. There are other, less savory possibilities. It could all be a fraud on the part of the consigners, a long con, or something completely innocent, and nobody wants to admit they are wrong. At this point, who knows? Certainly not me.
Forums like this, and sites like HeroComm, can be a tremendous resource for buyers, bidders, and researchers. They can, and do, affect auctions. Certain blogs can make or break items, and I think that can be a good thing. Nobody knows everything, and crowd sourcing some of the legwork can be tremendously helpful... or harmful. It's a great case of "let the market decide".
The problem is, when the offered item and provenance are contrary to the current wisdom, you'd better be ready to back it up. Judging by this thread, they haven't done a great job of that.