Wal-Mart (WMT -0.80%) has been on a buying spree since last summer, when it bought Jet.com for $3 billion. It's since snatched up several smaller e-commerce websites for less than $100 million each. Most recently, it's been in talks to buy upscale men's clothing retailer Bonobos for $300 million.

Despite the somewhat higher price tag, it follows the same strategy as Wal-Mart's other recent acquisitions. Wal-Mart is buying up retailers selling for a relative bargain. For example, just last year Bonobos was seeking funding at a $500 million valuation, but those talks seem to have fallen through. Wal-Mart could be getting 40% off retail for the retailer.

But Wal-Mart's new e-commerce acquisition strategy is very similar to its old acquisition strategy with Wal-Mart Labs. Between 2011 and 2014, Wal-Mart acquired 15 small companies tied in some way to e-commerce. The other thing most of them had in common was that they were selling for a bargain after failing to attract a new round of venture funding. None of them managed to significantly accelerate Wal-Mart's growth in e-commerce. Will this new strategy prove any more successful?

Wal-Mart boxes coming down a conveyor belt.

Image source: Wal-Mart.

Buying sales growth

One key difference in Wal-Mart's new acquisition strategy is that the online stores it's buying up will contribute sales directly to Wal-Mart's online sales. Its previous acquisitions largely supported backend technology for growing e-commerce sales organically.

Additionally, Wal-Mart's acquisitions are focused specifically on the high end of the market. Wal-Mart's head of e-commerce Marc Lore said the company is specifically pursuing retailers "in the categories where they are long-tail, high-margin products and harder-to-crack brands."

Wal-Mart has failed to attract those kinds of brands to its flagship store because it's often associated with lower prices and lower quality. Buying up companies like Bonobos or Modcloth will help Wal-Mart sell higher-quality goods at a higher margin.

But sales won't keep growing

Growth through acquisition isn't a bad strategy. The problem with Wal-Mart's strategy, however, is that these companies are selling for a bargain precisely because their growth is slowing. As such, if Wal-Mart wants its e-commerce sales to keep growing a year from now, it'll have to keep buying up these small e-commerce retailers.

On top of that, Wal-Mart could face backlash from these small boutique retailers' loyal customer bases. Numerous consumers threatened to take their business elsewhere on social media since reports surfaced of Bonobos' potential acquisition.

What's more, some of the top talent from these companies, such as Bonobos founder Brian Spaly, have already left to go onto more promising projects. So, Wal-Mart won't gain the advantage of bringing on a lot of great talent to support growth of its main e-commerce platforms, either.

There's a limit to the number of deals Wal-Mart can find. If it really wants to grow e-commerce, it needs to look for businesses that are selling at a premium because their growth is accelerating. It would cost more upfront, but it would set Wal-Mart up to keep growing e-commerce sales into the future. Jet.com is one such acquisition, which is why it was one of the biggest e-commerce acquisitions in history.

By comparison, Amazon (AMZN -0.29%) has been willing to spend big on its acquisitions. It bough Quidsi (diapers.com, soap.com) for $545 million, Zappos for $1.2 billion, Audible for $300 million, and most recently Souq.com (a Middle Eastern marketplace) for $650 million. While its acquisitions don't always work out (it recently shuttered Quidsi), Amazon's willingness to spend has resulted in better growth than Wal-Mart's.

In effect, Wal-Mart's new acquisition strategy suffers from the same problem that plagued its old one: The companies it's buying don't support long-term growth. Wal-Mart is spending hundreds of millions on companies that could just cause more headaches than revenue growth down the line, especially as it has to manage a growing basket of brands.

Investors should look for commentary from management during Wal-Mart's earnings call about how much e-commerce sales growth is coming from these kinds of acquisitions. In all likelihood, though, management will keep that information close to its vest.