WavyPhotons,
Ont thing that you may want to try is asking Costco if they can somehow get you in touch with customers that bought the same toilet. I know it's highly unlikely but you could ask that they do the contacting and ask that the contactee get in touch with you. Chances are that the chances would go up if it were a plumbing house and not a big store.
I suggest that you do that with mechanics, doctors, lawyers, dentists, sub-contractors, roofing companies, plumbing companies, pavers, window installers, painters, etc. You want to find out what others have to say about the person pr company. Since it's not a person that you're researching the typical resource is what others have to say about a product online. I typically start reading the worse reviews and work my way up to the best reviews. If you look at the spread of the reviews you should get an idea of the overall quality. For example, if more than 50% of the reviews are negative (read the reviews for the St. Thomas Creation Palermo, for example) you'll want to steer clear of that product. Next you want to consider why the responder said what he said. Was the cause not the toilet but the plumbing? Those reviews which are not of the product but the delivery, ie, cracked porcelain, you can readily dismiss as not being pertinent. Then you have to think of those reviews which are gushing due to initial impressions - they may change after a length of time, the more time the product has been reviewed, the better chances you will make an informed decision. In the absence of specific reviews you will have to get a feel for their other products, to get an idea of the company as a whole. Beyond that you will have to go with your gut. For example, St. Thomas makes a bowl called the Impala. The trap way looks nice. But that alone will not indicate the flushing efficiency, whether or not it has a sufficient bowl wash down, whether the rim holes have been engineered correctly, etc. If you do take a chance on a product you may want to open an account (keep it separately from your purchasing name (you can change your displayed name, btw)) and do a full review after living with the product for a while, for the sake of others.
Next, as you research on-line sellers, many have their own section for reviews. Apply the same rules, while trying to ascertain whether or not they are phoney reviews.
And, of course, applying one review to the rest of the product line may not be valid, for even Toto has been known to make a less than stellar product, as all manufacturers likely do. But, thanks to Terry's reviews and the reviews of its members, a general consensus can be formed as to what products are best and which products one should seriously consider purchasing.
Best of luck to you.