Marduk

I sell things on eBay but they are mostly my own possessions that I no longer want as I’m having a clear out. I’m not sure how I’m meant to prove this though. I don’t know if HMRC are going to end up contacting me to say they think I owe them something. I collect different toys, figures and other collectible things that are mostly kept in good condition and original packaging. If I eventually decide I don’t want a certain thing, I may be able to sell it in ‘new’ condition, but I don’t know if this could be used against me to say I’m trading? In most cases, I can’t prove that I didn’t buy to intentionally sell for a profit. I'm also selling some old train sets that I inherited, so I have no record of the original cost. I'm worried the government are going to try to tax me on the full value of the sale which probably won't be much more than the cost when it was originally purchased 10-20 years ago! I don’t have any proof of the original purchase so I can't prove I didn't find them at a car boot sale for £5. Just hoping for a bit of info about how to deal with this. Will I just be contacted eventually by HMRC to say I owe them money unless I can somehow prove I don’t? Thank you.