Hi,
The disposal of personal possessions, falls under the rules for Capital Gains Tax. In a tax year where the value of your disposals, minus acquisition and disposal costs, is greater than the annual exempt allowance of £6000 in the tax year 2023 to 2024, Capital Gains Tax is payable. You can see guidance regarding chattles and sets of assets here:
CG76631 - Chattels: sets of assets: special rules
Capital Gains Tax on personal possessions
The selling platform will be required to report the disposal to HMRC, when a certain number of disposal have occured.
The rules for disposing of personal possessions, will remain unchanged and gains will be subject to Capital Gains Tax rules. Where you acquire assets to intentionally send on, then this is not personal possessions, but trading and should be declared as self employment/sole trader to HMRC.
You can see more infoirmation about collections here:
CG76870 - Chattels: particular assets which are chattels
Thank you.