The only concession I am prepared to make here, is that the designer (and GB runner) may be (and usually is) responsible for getting other worldwide vendors on board, and they may not choose wisely, but if there is a problem with one particular vendor, it doesn't necessarily follow that the entire GB is a car crash and buyers elsewhere may not even have a problem at all. Then in that instance, it's that one particular vendor that created an issue, not the designer.

There are just too many variables to say the designer (usually the person who advertises the GB and generates the interest through posts and social media awareness) can't always be the person who is to blame if something totally out of their control happens. From a legal point of view, the person ultimately responsible if it comes to refunds etc. would be the vendor you "bought" them from, and as most GBs have multiple vendors, even that is not as straightforward as you seem to be suggesting.