eBay's (NASDAQ:EBAY) turnaround effort might take longer than investors had hoped. The e-commerce platform announced first-quarter results that kept the company on pace to meet its broader 2018 financial targets. However, the latest operating trends contained a few signs of struggles ahead.

Let's take a look at the two biggest ones.

A person holding a credit card while using a laptop.

Image source: Getty Images.

Growth challenges

eBay attracted more buyers during the period, with its base of active shoppers rising to 171 million. Its expansion rate slowed to 4%, though, after holding at 5% in each of the previous four quarters.

Chart showing rising buyer pool over the past 6 quarters.

Image source: eBay investor presentation.

eBay needs that buyer pool to keep growing at a robust pace so that it can attract more inventory to its marketplace. The slowdown can't be pinned on broader industry struggles. Amazon's (NASDAQ:AMZN) product sales expanded by 33% during the period, after all, compared to eBay's 7% boost.

Looking behind that figure, the core U.S. marketplace business slipped to a 7% increase from 8% in the prior quarter, while things sped up slightly in international markets. eBay's unit volume also slowed to its weakest pace in more than a year even though overall merchandise volume expanded at a steady 7% rate. These numbers are roughly consistent with management's broader goals, but they don't point to accelerating growth.

Profit setback

Similarly, eBay's profitability remained healthy but took a small step backward during the period. Its transaction fees, the company's main source of earnings, dipped slightly to 8.6% from 8.7%.

The platform shelled out more for advertising and marketing, which management said was a result of their efforts to better communicate eBay's value proposition to shoppers. Together with added investments in product development, that boost lifted operating expenses to 51.1% of sales from 49.6% last year.

EBAY Operating Margin (TTM) Chart

EBAY Operating Margin (TTM) data by YCharts.

On the profitability front, the company still trounces fully integrated rivals like Amazon and Walmart, which post low-single-digit operating margins. But eBay's earnings power is looking a bit less robust right now as operating margin fell to 27% of sales from 28% a year ago.

Expect more bumps ahead

eBay has tried to make it clear to investors that the business could experience periods of volatility like this. After the company logged its best growth pace in almost three years last fall, CEO Devin Wenig said in a conference call that "there's still a lot of work ahead of us, and we recognize that making significant product changes can have a big impact on our ecosystem."

Wenig said that the company always aims to keep trends steady but warned, "We don't expect growth to always be linear as we favor decisions to drive long-term success even when that pressures short-term results."

These latest operating figures look like an example of that risk playing out. eBay made several tweaks to its ecosystem this quarter, including changes that impacted how its products showed up in internet search results, how its inventory was marketed to buyers, and how consumers interacted with its brand.

The moves didn't knock the company off its broader growth goals, and so investors can still expect to see sales gains of about 8% this year as adjusted earnings land between $2.25 and $2.30 per share. Those figures would mark a continuation of eBay's multiyear rebound effort. Yet they wouldn't be the type of surging gains that many investors might have expected as they pushed the stock significantly higher in recent months.

John Mackey, CEO of Whole Foods Market, an Amazon subsidiary, is a member of The Motley Fool’s board of directors. Demitrios Kalogeropoulos has no position in any of the stocks mentioned. The Motley Fool owns shares of and recommends Amazon. The Motley Fool recommends eBay. The Motley Fool has a disclosure policy.