Wholesale retailer Costco is making headlines as it takes the US Government to court, alleging that it's owed money over damage caused by tariffs.

Costco Wholesale ( COST 0.18%) is having a rare off year. It's a stock that almost always beats the market, and as you go back in time, the outperformance keeps getting wider. However, Costco stock is roughly flat this year, even as the S&P 500 index has soared 17%. Is this a great time to buy? Or a signal to stay away?

Costco stock dipped 0.5% in after-hour trading to $917.25. Shares are roughly flat this year, gaining just about 1% while the S&P 500 has increased 16%. Costco Wholesale released both its November and fiscal first-quarter sales. Both rose at a healthy clip, fueled by growth in e-commerce.

The Costco return policy is very generous and flexible, but there are some exceptions and rules that Costco shoppers should be aware of.

The good news is that a major shift in behavior among Costco members indicates a better all-around shopping experience. When Costco announced several months ago that it would open its doors to Executive members early, that decision was met with some backlash.

Valuation can be a powerful tailwind for investors. However, this requires the starting valuation to be attractive, allowing room for multiple expansion. Costco doesn't fit the description. Its shares trade at a nosebleed price-to-earnings ratio of 50.

So Costco is probably not going to anger too many customers by speaking out against a trade policy that is unpopular in the first place. Costco didn’t appear overly concerned: It used some choice words in its lawsuit,