The wine selection is all over the board. To shop at GO in general, and this applies to wine as well, you need to be the sort of person who can ignore the chaff and focus in on the gems. Not everyone is good at this and fail to see the bargains to be found. Some stores have better wine buyers than others and some like Redwood City, Concord and Rohnert Park have dedicated staff in the wine departments who can help customers and go for the better grade selections.
I have not run into any storage faults buying at the SF Bay Area stores, but then again I'm careful to check the bottles for signs of heat damage. Much of the wine on the shelves is from past vintages and should have been consumed months or years ago. Anything that is of current vintage tends to be dreck that couldn't find shelf space, so that can be one of your guideposts.
I've had good luck with imports. The better European wines are fine with more bottle age in the warehouse past the release date. I look for interesting DOCs and appellations, and check who the importer is and go with the quality names. Some of the best buys have been for brands that have changed importers and the old importer or distributor dumps the stock it had on hand for pennies.
And keep in mind that Grocery Outlet has a liberal return policy. You can pull the cork in the parking lot to test the condition of the wine, and take it back for a refund if it's over the hill or run inside and buy more if you like it. The good stuff doesn't stay on the shelves long, just a few days. . . although I suspect that the Corton-Charlemagne in the Salinas store isn't moving that fast at $100.
Each month the SF Bay Area 'hounds post their finds at Grocery Outlet stores. This includes other food as well as wine. Keep an eye out for the thread, as there will usually be a few wines highlighted and you might find them at your local store. Here's my latest tasting note, the La Louviere rouge purchased from Grocery Outlet.
I've had miserable luck at grocery outlet but a friend who checks the Reno store finds some real gems.
On the other hand, Chowhounds seem to find lots of good wine at the California Grocery Outlets, particularly the one in Berkeley. Chowhound Melanie Wong has posted about the gems she has dug up at ridiculously low prices.
One concern is how well they have been stored before they ended up at Grocery Outlet.
All in all most of the wine there tends to be industrial grocery store wine but people who know their stuff can find some great bargains.
Perhaps Melanie will chime in here with some suggestions of what to look for right now (it's up to the store manager to decide what to stock) or maybe you can contact her some other way.