There is a distinction to made here about what types of yurts we are talking about. Since everyone here so far is talking about the modern day, contemporary, North American yurt, I suspect that is what kind of yurt this forum will focus on, even if not exclusively. So that's what I will focus on here, clearly leaving handmade, more traditional yurts out of this summary.
Perhaps the largest benefit of the North American style yurt is the potential for predictability of the structure. It is only because of that potential for predictability, and the fact that some manufacturers have paid the costs of proving that predictability, that many areas now allow yurts to be permitted. Some yurt manufacturers have capitalized on that and have gone into business selling, on a mass level, yurts of inferior design, that are dangerous because they are not completely thought out, and these threaten the permit-ability of yurts on a large scale. It is a short sighted, greedy mindset, to say the least. Because of that, and to protect the permit-ability of these styles of yurts for future generations, as well as protect the industry as a whole, I think it's important that a manufacturer have full structural engineering specs run on their yurts. It's a belief that is shared by many in the industry.
That said, it's as you say Jafo. I doubt any manufacturer will give you, a public forum, their full specs. That would allow other people or companies to be able to easily ride off their costly and painstaking work. They can, however, show proof that they have the engineering done and provide a summary of wind speed, insulation
, weight load bearing, and fire resistance ratings. That is often all on the summary page from the engineering firm that I mentioned. Moving into the future, I believe that this will be mandatory in most places, as more and more places begin to accept IBC (International Building Codes) or UBC (Universal Building Codes). In my experience, a company that has done this step is a company that has taken the largest first step in showing that they are a conscientious, reputable manufacturer.
Other things to be sure of is the reputation of customer service. Do they handle things when they go badly, do they just blow you off completely, or fight to escape responsibility?
Are there major complaints against a company with the Attorney General or the BBB of their area?
What is their warranty on the roof and the rest of the structure?
Do they know basic, universal building codes?
Will they help you wherever possible with your permit process?
Do their yurts meet IBC codes?
Look at the standard things included.
Ask for accurate shipping costs of the day (Estimates often tend to be low balled to avoid sticker shock - The yurt industry does not control shipping costs, but some companies have ways of significantly dropping your shipping costs)
If you're interested in catching water, ask about the gutter systems. Have they been tried and tested? Get feed back from other customers.
Insulation is a big one for you folks in colder areas. Will their insulation meet r-value codes? If they don't know, that's a red flag.
Good yurt companies stand head and shoulders above the bad. It isn't difficult to figure out. If you're paying the lowest price on the market, there's a reason for that. The company has not likely paid their dues in testing, research, etc. and you, the customer, will be part of their trial and error process.