eBay (NASDAQ:EBAY) investors had a fantastic 2020, with the stock price comfortably outpacing the broader market during the pandemic-fueled e-commerce boom. Sure, companies like Amazon and Shopify posted wider gains. But eBay's nearly 40% share-price spike reflected some major operating wins and kept it ahead of other huge online businesses, including Walmart.

Investors are about to learn exactly how well eBay did in 2020 when the company announces its holiday season results. The strength of that performance, along with management's official outlook for 2021, will determine whether the stock continues its winning streak into the new year.

Let's take a closer look at the company in advance of the fourth-quarter earnings report's release on Wednesday, Feb. 3, and what investors should watch for.

A young woman celebrates behind a laptop screen.

Image source: Getty Images.

Merchandise volumes and conversion rates

eBay's core growth metric is the volume of merchandise moving through its platform. Soaring results here formed the basis for last year's stock surge. Volume had been flat or declining in the quarters before the pandemic struck but shot up to over 20% year over year as commerce stampeded to online channels beginning in late February.

This quarter's report will answer big questions around the sustainability of that spike. Volume gains year over year slowed to 21% in Q3 from 29% in the quarter that captured the most intense period of retailing shutdowns. For its part, management in late October forecast gains in the low double-digit percentages. However, eBay easily surpassed its last quarterly outlook, and investors are hoping for another beat this week.

Other indications of healthy market share would show in an expanding buyer pool and robust conversion rates for its product pages. CEO Jamie Iannone should comment on both these metrics on Wednesday.

Cash and profits

eBay's asset-light operating model restricts its growth potential a bit as compared to Amazon, but the trade-off is higher profitability and impressive cash flow. Earnings more than doubled last quarter as operating margin surged thanks to the combination of higher sales, lower expenses, and an uptick in seller transaction fees.

Wall Street is expecting more gains ahead in this area, with reported earnings set to rise to $0.83 per share compared to $0.66 per share a year ago. But the more useful figure to follow is cash flow. eBay generated $584 million of free cash flow in Q3, and the company needs more success here to meet management's goals of investing in the business while paying down debt and sending more cash to shareholders through dividends and stock repurchases.

The 2021 outlook

Iannone and his team will be looking at an unusually wide range of potential results as they craft their official 2021 forecast. Organic sales likely increased by at least 20% in 2020 compared to their initial prediction targeting a flat result. That boost sets a high bar for growth this year, but it also gives the marketplace giant momentum in a quickly growing industry.

The good news is eBay already showed off a few impressive competitive advantages at a time when sellers were looking for new platforms they could use to connect with their customers during COVID-19.

The company's main challenge for 2021 is convincing these small businesses to stick around, mainly by making the platform more popular with buyers and easier for sellers to use. These successes are the key to eBay protecting its positive momentum in what's likely to be a competitive selling period ahead for the e-commerce industry.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.