I am a taster at several competitions and I also sell wine wholesale. There are only a handful of professional tasters in the world, and most of them make their living by tasting and rating wines and publishing their notes and scores. (James Laube, Robert Parker, Anthony Dias Blue, Michael Broadbent, etc.) Their careers are in the wine PUBLISHING business, so in addition to being extremely knowledgeable about wine also requires the same career track and skills as any professional writer.
Major hotel, airline, retail chains and restaurant chains have dedicated buyers who evaluate hundreds of wines for purchase for their respective companies. There are quite a few of these jobs, but I must caution that being a "dream job" they are hard to get and most require years of experience in the wine business (though as you might imagine, not everyone who has one of these jobs is qualified for them).
Within wineries the tasting is done by the production staff. This is at variance to the practices of food manufacturers and beer and spirits manufacturers who often employ tasters to ensure consistency and to develop new products.