Jane Ruffino: Bricks-and-mortar giants like Walmart are entering business online

So it’s a good time to count the cost of free trials and low prices from ‘start-ups’

Last week, Walmart bought online retailer jet.com for $3.3 billion. Jet was established in 2013 by the founder of retailer quidsi.com. Quidsi was bought by Amazon after Amazon undercut Quidsi’s prices too much for the start-up to compete. A couple of Quidsi’s founders started Jet to compete with Amazon on prices.

Its differentiator was initially that it would make a profit only on Jet’s $50 annual membership fee. The site launched in July ...