SEATTLE — Frustrated you haven’t received that package from Amazon yet?

You’re not alone.

The crush of coronavirus-fueled demand for online shopping clogged Amazon’s operations, flooding it with orders from homebound customers that it was ill-prepared to handle. That led Amazon to prioritize sales of essential items, and left many third-party merchants on the site to take on shipping that the e-commerce giant had previously managed for them.

The results haven’t been pretty. Amazon shoppers are fed up with those third-party sellers on the site at levels rarely, if ever, seen, according to data culled by Juozas Kaziukenas, chief executive of e-commerce research firm Marketplace Pulse. Shoppers, who can register opinions about the service received from third-party merchants as negative, neutral or positive, are clicking “negative” at the highest levels Kaziukenas has ever recorded.

“How much it broke and how quickly it broke is much larger than people realize,” he said.

Experts who work with the sellers say the problem largely stems from a decision Amazon made March 17. Typically, merchants ship their goods into Amazon warehouses, and then the online retail giant completes the orders. But as the coronavirus spread, Amazon delayed shipping of nonessential items to focus on getting customers toilet paper, bleach and other household staples.

Customers could get other items from Amazon, but they’d have to wait weeks. So merchants that didn’t want to see sales evaporate handled shipping items themselves.

Now customers, who’ve grown accustomed to speedy shipping from Amazon, are increasingly griping about delays, packages never arriving and damaged items in a flood of negative reviews.

More than 11 percent of reviews left for sellers in the past 30 days are negative. That’s nearly twice the level of frustration vented by shoppers regarding Amazon’s third-party sellers during the holidays, when customer anxieties spike over not getting presents on time, Kaziukenas said.

Third-party merchants accounted for 58 percent of all physical merchandise sold worldwide in 2018, the last time Amazon disclosed the figure.

Finance chief Brian Olsavsky attributed delays in items from Amazon’s warehouses, both from third-party sellers and from Amazon-sold goods, to “picking and packing and getting it to shipment,” in a call with the media last month. And Amazon spokeswoman Cecilia Fan said some of the measures Amazon took, such as social distancing among its warehouse staff and prioritizing essential items, better protected its warehouse workers even as they reduced the company’s efficiency.

“We know customers want their deliveries as quickly as possible and we are working hard to return all products to faster delivery speeds while helping keep our employees safe,” Fan said in an emailed statement.

(Amazon chief executive Jeff Bezos owns The Washington Post.)

Over the years, Amazon trained customers to expect delivery of a wide range of products within a day or two, as long as they subscribed to its Prime program, which costs $119 a year for most U.S. members. Speedy shipping, though, generally required third-party sellers to send inventory to Amazon’s warehouses and participate in a program called Fulfillment by Amazon, or FBA, in which the company ships products on its own or through carriers that prioritize its packages.

“One reason why Amazon put FBA in place is because sellers aren’t very good at doing this,” said James Thomson, a former senior manager in business development at Amazon and now a partner at brand consultancy Buy Box Experts. “Amazon has wired us to think we can have everything we want when we snap our fingers.”

As the coronavirus spread and pushed consumers to shop more from home, Amazon’s customers flooded the site with orders for household staples. Amazon struggled to handle the demand surge, in part because its warehouse workers often called in sick. Some raised concerns about workplace safety, including productivity quotas that could discourage safe sanitary practices. The company also fired workers who spoke out about the conditions, though the company said the firings were related to violations of company policies.

Meanwhile, sales jumped 26 percent in the quarter that ended March 31, to $75.5 billion. In a statement at the time, Bezos described the coronavirus crisis as “the hardest time we’ve ever faced.”

In response to the virus, Amazon has modified policies, providing warehouse workers face masks and checking their temperatures as they start their shifts. It also hired 175,000 employees for its warehouse and delivery operations.

Amazon also took the March 17 step to temporarily stop accepting nonessential items from third-party sellers. Products already in its warehouses that weren’t in those high-demand categories were de-prioritized, often showing up with delivery times several weeks out.

Maxxima, a lighting products company in Hauppauge, N.Y., already shipped orders for its listings on Home Depot and Walmart, but sent items in to Amazon. When Amazon shifted Maxxima’s products to nonessential status, customers started canceling orders after learning of the lengthy shipping times, said Senior Vice President Dov Sassoon. The company also saw a spike in orders of its products on the e-commerce sites of Home Depot and Walmart, where orders shipped faster.

“People don’t want to wait,” Sassoon said.

Rather than lose revenue from customers putting off purchases or looking elsewhere, Maxxima, like many third-party sellers, opted to start handing its own Amazon shipping, too. Sassoon acknowledged that it took Maxxima “a few days to dig out of our hole of orders” when it added in the sales from Amazon.

As delays played out across Amazon’s marketplace, frustrated customers, who routinely began — and often ended — their shopping on the site, took business elsewhere. Mark Donne, a video producer for a tech start-up in the Boston area, needed to order headsets for conference calls as the pandemic forced him and colleagues to work from home in late March.

“I went to Amazon first to check and see,” Donne said.

The Logitech product he wanted was available, but it wouldn’t arrive for several weeks. So Donne visited Logitech’s website, and the order arrived 12 days later. Last week he needed a monitor to view videos he shoots for YouTube. Even though Donne has been a Prime member for nearly seven years, he opted to buy the monitor from B&H Photo & Electronics.

“I love that @BHPhotoVideo can get me my order in 2 days for free. But I pay @amazon a yearly fee and Prime shipping is 1-2 weeks,” Donne tweeted last week.

Kaziukenas has seen that sort of frustration mount. Of the 913,000 seller reviews left worldwide in the 30 days that ended May 18, shoppers clicked “negative” 11 percent of the time, up from 6 percent of the 350,000 reviews a year earlier. Even during the holiday season, negative reviews rarely top 7 percent, according to Kaziukenas’s data.

Sifting through the written comments, he found that 46 percent of the negative reviews included words related to shipping, such as “not received,” “never shipped” and “broken.”

Given the quick shift in shipping, Amazon took steps to cut sellers some slack. The company has nixed negative reviews for sellers when it was responsible for shipping delays from its warehouses. And Amazon temporarily paused enforcement of rules regarding sellers’ delivery performance, though those will resume June 1, Fan said.

With the hordes of new workers and policies designed to improve workplace safety, Amazon is inching back toward normalcy. On April 20, the company eased its warehouse receiving restrictions, accepting limited quantities of products from sellers so as not to overburden its taxed system. And last week, Amazon removed quantity limits altogether, spokeswoman Fan said. While products such as Quilted Northern toilet paper are now easier to find on the site, Purell hand sanitizer remains unavailable.

Fan declined to say whether the company will refund Prime membership fees or offer discounts on them next year, given the shipping delays.

Amazon, which said it’s planning to spend $4 billion this quarter to address the issues that clogged its operations, is better positioned to weather the crisis than many of its bricks-and-mortar rivals that have seen sales shrivel. Macy’s shuttered all of its 775 stores in March and furloughed most of its 125,000 workers, and Neiman Marcus sought bankruptcy protection earlier this month.

Still, Amazon’s decisions have created headaches for many of its sellers.

When the Fort Pierce, Fla.-based company Lawn Chair USA opted to ship lawn chairs sold on Amazon on its own, it found that buyers were still seeing one-month shipping times, said co-owner Andrew Pokrandt.

That’s because Amazon gave preference to items stocked in its warehouses, giving them top billing in the buy box, the piece of digital real estate on product pages where customers add items to their shopping carts. Pokrandt had to raise prices on items in Amazon’s warehouses so the products he shipped got priority.

The company’s sales rebounded, but Pokrandt has seen his margins shrink because he can’t match Amazon’s shipping rates.

“They are a lot smaller, but we’re still profitable,” Pokrandt said.