amanda blowers

I have tried calling the helpline and been given different answers to the same question. I sell on ebay and vinted and aware a total will be sent to the HMRC as I am in the reporting amounts for each. I sell items that I bought and have used personally in my family and sell as used, not making a profit on most but some I have. I sell items that I have bought to help my collections and sold off the others both new and used, sopmetimes I sell them straight away sometimes after a long period. Some items I make a profit on as I know are collectable and I usually have bought USA. I have been told to include everything so the total matches my ebay and vinted totals as I use one account for each. Some of my items I cant find receipts for so I have to take the full amount as profit ? thank you advice welcomed as want to getit right and is taking some time to get the info needed.