From the summer, the site will guarantee the speedy delivery of 20 million products from certain sellers who currently meet delivery promises.

If items don't arrive on time, eBay will refund shipping or give shoppers a voucher if delivery was free.

One analyst questioned whether the move would appeal to eBay customers.

"It comes as something of a surprise," said Bryan Roberts, a retail analyst at TCC Global.

"Quite a lot of what is purchased through eBay is discretionary, it's not usually urgent health or food products, for example."

Another new feature will allow buyers to filter products that will arrive even more quickly - within one or two days' time - when browsing the site.

Trusting the seller

EBay currently relies on millions of sellers - from individuals to larger businesses - to organise deliveries.

"There are so many great sellers on eBay delivering an incredible shipping experience where they deliver in two days, and even next day, so the ability to highlight Guaranteed Delivery will further increase customer confidence and satisfaction," said Brett Thome, who runs VMInnovations, which sells products via eBay.

The new move depended on sellers being able to stick to the promised delivery times, said Mr Roberts.

"It does involve them putting a bit of faith in their vendors," he told the BBC, "but it could pay off for eBay and enhance their position."

The site has experimented with fast delivery promises before, with varying success.

In 2015, it ended a pilot programme in the US called eBay Now that offered one-hour local deliveries in certain cities.