Cullen and Reyes agree that Costco has a great selection of vino, with especially good coverage of California and other domestic US wines.
But you shouldn't think of the warehouse chain as your one-stop shop for the exact, specific wine that's on your mind.
"Costco is almost like a curated wine collection for you," Cullen told Business Insider. "You're not going to go there and find whatever bottle you may be looking for. If you're looking for a Chardonnay, you're going to have to buy whatever Chardonnay is there."
Reyes recommended calling ahead if you've got a particular wine in mind, to make sure it's in stock.
Don't be intimidated by the more expensive options.
Costco is famous for its value-oriented approach. And Reyes and Cullen both say that the chain boasts quality wines for good prices.
But Cullen said that you shouldn't be afraid to occasionally splurge on a more expensive wine.
"I think it's a great place to buy more expensive wine," he said. "The average price savings that you're getting — it's magnified as you spend more."
He gave the example of the 2013 vintage of the Joseph Phelps Insignia. Cullen said the wine could go for around $225 at most retailers, but Costco members could pick it up for around $199. Cullen happened to get an especially killer deal on the wine.
"I was able to get that for $179, which is a pretty good deal," he said.
Don't be afraid to dig around.
You might feel a bit silly tearing through the wine bins like you're searching for your dropped keys. And Cullen said that he feels that people think he's "weird" when he starts digging around in the wine section of the warehouse.
But he doesn't let that stop him, and for good reason. Cullen said that different vintages are often mixed up in the bins together. If you forgo rooting around, you risk missing out on the best vintage.
That's because different vintages tend to be thrown in the bins together.
"Don't just grab the first bottle," Reyes told Business Insider. She said that while vintage might not matter as much for lower-end wines, for high-ticket bottles it's far more crucial.
Cullen also recommended checking beneath the wooden racks, where you might find a forgotten bottle of an otherwise sold-out wine.
Either way, it's a mistake to leave the warehouse without doing a thorough investigation of the available bottles.
Don't assume a certain type of wine will be around forever ...
Even beloved Costco products might be here today and gone tomorrow. The chain's wine section is no different.
"Sometimes, there are unique wines that are hard to find that will just show up and then they're gone," Reyes said. "And then they never come back again, so that's kind of intriguing."
"If you see it and you really want it, you'd better buy it right away, because it might not be there when you come back," Cullen said. "That is the Costco way, and that definitely applies to wine."
Cullen and Reyes both check back at their local Costcos relatively frequently, to check out the new products. Sometimes, they're surprised to see an old favorite return.
"Wine will disappear and then they'll randomly come back three months later," Cullen said. "You're like, 'Whoa, look what's back.' People love that."
Don't buy a whole case before sampling the wine.
Costco is famous for selling its products in bulk. That's why Reyes recommends purchasing a bottle of a new wine before springing for an entire case.
Because while it might be tempting to purchase a case-load of wine when it's on rebate or when you've enjoyed previous vintages, you never know.
"If you do like it, come back before the rebate expires," she said. "And if you like the new vintage the same, go ahead and buy your case."
Don't be afraid to try new things.
Cullen said that when he's shopping for wine at Costco, he tries to avoid constantly grabbing the same things over and over again.
"Don't be afraid to try something new," Cullen said. "Don't just say, 'I love Chardonnay, I'm only going to stick with Chardonnay.' You might be missing out."
Don't go it alone.
Costco members actually have a few resources at their disposal when it comes to purchasing wine at the warehouse.
Some Costcos employ a resident wine advisor to help members with selecting the perfect bottle of red, white, rosé, or bubbly.
"They have no vested interest in promoting a certain wine," Reyes said. "Their goal is just to increase the wine sales. They're good resources. They have all the insider info without an ulterior motive."
Cullen added that the Costco Wine Blog's forums are also a good space for sharing tips and making and receiving wine recommendations.
"It's such a good community of people," he said. "There's virtually no haters. It's 99% positive people on the same mission. That's made it more fun."