For the professional brewers over here

[Zebedee]

you can have an adequate look at excipient usage in any finished product by GCMS testing via a real laboratory, and if you do so, you'll find those products to be completely devoid of guaiacol.

I’m not sure if you could actually use guaiacol without customers being aware of it simply by its distinctive scent - I’ve know homebrewers say they’ve used it at just 2% & it’s still easily detectable.