Costco will be reporting its fiscal fourth-quarter earnings after the closing bell on Thursday, with Wall Street looking for EPS of around $6.53 to $6.55 on revenue of roughly $94.9 billion.Those numbers matter, but I think there is a more interesting question sitting beneath that. That being:Is the US consumer actually starting to weaken, or are households simply becoming much more selective about where they spend?Heading into the earnings call, the latest US retail sales data would argue against any outright consumer collapse. Retail sales rose 1.2% in August, comfortably beating expectations, while spending excluding gasoline also remained strong. But that resilience is being tested by a much less comfortable inflation backdrop, with headline CPI running at 3.4% and gasoline prices up 27.4% from a year earlier.And that is where Costco becomes useful as a real-time consumer gauge.The early sales numbers already look solid. Costco has already reported fourth-quarter net sales of $93.9 billion - up 11.3% year-on-year. The more important clues on Thursday will come from traffic, basket size, memberships, and what management says about discretionary spending.In the last quarter, shopping frequency increased 2.4% while the average transaction rose by 7.3%. And paid memberships reached 82.9 million, with US and Canada renewal rates holding at a very healthy 92.2%.That does not look like a consumer disappearing. If anything else, the behaviour looks increasingly value-driven instead.Costco has already said members are responding to higher fuel prices by using its gas stations more frequently, while the company has also cut prices on selected everyday items to reinforce its value proposition.That did come at a cost as reported gross margin was compressed by 21 bps in the last quarter, although it was roughly flat once you exclude gasoline effects.As such, I would pay less attention to whether Costco beats EPS by a few cents and more attention to the composition of spending.If the signal from traffic, renewals and essential category demand remains firm while discretionary purchases soften, the message may not be that the US consumer is starting to break down.It may simply be a case that households are still spending, just that they are demanding much more value for every dollar. This article was written by Justin Low at investinglive.com.