Guild as in the Guild of Irish Woodturners - no idea what that offers it's membership towards what is being discussed in this thread, but they are a Guild.
There is the Worshipful Company of Woodturners, one of the Livery Companies, but as I understand it they are the holders of and successor to the Guild of Turners. So there is such an organisation already. Having said that there membership all up is just over 200 and I think membership is by invitation only.
If it is their remit to promote the Craft of Woodturning surely it should be through them that any such certification should be issued. I'm not saying set amateurs and hobbyists against the Professional Turners (RPT), there is a huge difference between the many of us and the few turners who do truly earn their living from turning.
But to be assessed, to be accepted as a turner of a known standard, who is capable of producing work of a certain quality, to be able to display a certificate to that effect from an organisation such as Worshipful Company of Woodturners, that would mean something.
Not some self serving, made up guild.