Currently you are governed by consumer protection law.
Selling on line you are governed by additional Distance selling Laws and Financial services act which govern each payment you may receive.
I am a seller of clothing and footwear on eBay and from what I understand electronics along with Branded computers are at a much high risk as item defective or item not as describes (INAD) cases.
Law does not require your buyer to prove his case and you the seller must accommodate return and pay return postage and issue a full refund to buyer. Return period on eBay's platform is limited to for 14 to 30 days after item is delivered.
In addition a buyer can make a claim defective or INAD with their bank including Pay pal and Credit card issuer up to 180 days from date of payment and this case is commonly referred to as Charge back. Seller is required to accept a return and issue a full refund and buyer is required to send the item back via Tracked & signed service to sellers address and if track and trace website shows item delivered then sellers is not consulted and case is closed in favour of buyer and sellers account debited.
Having pointed out all pitfalls of selling on a platform/ Online a much safer best would be for you to consider creating your own website and instead of paying fees to a platform you spend that money on advertising and as you sell computers I suspect you must know how you or one of your employees can get social media platforms to work to your advantage. eBay outlet may work better for you to clear out you old redundant stock where it really does not matter if you gat abused.
Whatever you choose to do I wish you best of luck.
