The internet giant has dubbed December 29 as "Boxing Up Day" because of the peak in searches by Britons looking for items to help with goals such as stress relief or weight loss.
Households across the UK receive more than £850 million worth of gifts they do not like each year, according to eBay's research.
A survey of 2,000 adults found that eight out of 10 believe Christmas is the best time to declutter and that the process of making space makes them feel more positive about the year ahead.
One in five said they would use the money made from selling Christmas gifts to fund their plans for the new year.
Those surveyed planned to spend an average of £511 on items including new clothes, hairstyles, fitness equipment and DIY.
The auction site claims that between 9pm and 10pm on December 29 is the best time to sell unwanted presents because it sees a peak in searches, with up to one every eight seconds.
A third of the survey group said that by this point "Christmas fatigue" has set in and 81% said they were starting to look to the year ahead.
Last year Britons bought more than one million items on the site between December 27 and 30 at a rate of 173 products per minute, or three every second, according to eBay's sales data.
Will Weightman, senior director, consumer selling, eBay UK, said: "The period between Christmas and the New Year is an incredibly busy listings period on the site.
"Normally at this time of year people are looking for ways to make a bit of extra cash and fund the things they want to do in the new year."
Among the most common items listed for sale over the Christmas period were home decor such as lamps, vases and soft furnishings, power tools and smartphones.