Confusion over HMRC rules and Ebay and NIN

I have just been told by the online marketplace eBay that if I do not give them my national insurance number — as requested by HMRC rules — then my funds from items sold will be frozen, not paid out to me, and my account with them jeopardised. This is alarming, years ago, the government told ALL UK citizens not to divulge our national insurance number (NIN). More importantly, perhaps, I am NOT a registered business'seller' but rather a private one having a huge clear-out your attic and selling unwanted items using eBay — I think I have sold so far around 31 items in the past tax year. Please clarify HMRC rules and my obligations with regard to the above.

Hi InForaPennyinForaPo,
Please refer to:
Check if you need to tell HMRC about your income from online platforms
Thank you. 

Thank you for your response. However, I had already checked ALL information, including that shown in the link you provided, by HMRC and it didn't help at all. Hence, why I asked this question a week ago. Please clarify (that is what I assume this forum was intended for) ASAP.

Hi 
This forum is for general queries only and is intended to help you self-serve hence the advise to check the link previously given.
Thank you.

This is an extremely unsatisfactory and unhelpful answer, considering the purpose of the HMRC Customer Forums. My query can be construed as a general enquiry, as proven by other questions on this forum similar to mine that HAVE been answered. Ii am not asking for specific advice tailored to my individual circumstance, rather, someone who would be in a SIMILAR situation: ****Do 'private sellers' on eBay clearing out their homes/attic and selling unwanted items using eBay have to under law and directed by HMRC disclose to eBay their national insurance number?**** The information provided in the HMRC links do not help — indeed, it seems to contradict itself — and therefore the HMRC Customer Forums are there for that very purpose — to answer where the links and information cannot. Could you please forward to someone who is able to help ASAP?