If you want to work with a wine store or distributor, I can't imagine that you need any certification. Most people in those places have no formal certification. The main requirement is that you can sell. And of course, everything that goes with that - personable, dependable, curious, hard working, etc.
I've been tasting a few thousand wines annually for years. Of course, that meant tasting regularly at home, with friends, in groups, at trade tastings. Also visited numerous wineries in various countries and read whatever I could. I guess I was a little obsessive about it, but that's what happens if you like something.
And after a few years you learn. Eventually I was recruited by a few distributors and retailers from a career that had nothing at all to do with wine, and finally I took a job with an importer to see if I really liked working in the business.
My advice is to simply start to work in a store as a part-time thing, maybe weekends or evenings. You'll get to taste whatever the distributors bring, go to trade tastings, etc., and soon develop a fairly good knowledge of what's out there. And you won't have spent a lot of money to do so.
You're not going to get as broad a knowledge, but query as to whether you really need that to do what you are planning. Knowing about 1982 Bordeaux is nice, but not necessary if you aren't going to sell it.
There is absolutely nothing wrong with getting a certificate, but you can very easily learn a lot on your own. It's what people did before the craze for certifications anyway. Eventually, if you find you want to work in a different area, you might want to learn about service, for example. That might mean taking a class. But for retail, I can't see it.
Best of luck whatever you do!
Good luck to you!