I’m sure this is the case with at least some of the Exhibition and Society wines. While there are no doubt minimum quality standards that the wines must meet, if the wine meets those standards the Society will likely be obliged to purchase the wine that has been allocated to it.
Of course, the position is similar with all wine that the Society purchases en primeur. The buyer may have tasted the wines in barrel, but they will not have tasted the final product before committing to buy it. We just have to rely on the experience of the buyer to be able to predict how the wine will turn out. I really don’t see this as being fundamentally different to the situation where the buyer has been more actively involved in the blending, for example, Pierre Mansour and the La Rioja Alta 874 Selection:
At the end of the day, I am relying on Pierre’s skill and judgement to help create a blend that will be attractive to me and other Members.