I guess it depends on what specific purpose you will be using the designation for... it's really in the eye of the beholder.
If you want an interwinery discount, at least from me, you have to be an employee or principal of a winery. I know some wineries only offer it to principals. Some offer it to anyone remotely connected to the industry... restaurant employees, sales, etc.
If you want to attend trade only events, it will depend on the event organizers. If you just start a blog, your press pass may be slow in coming. Become Alder Yarrow who writes Vinography.com and you can probably be considered "the trade."