Soldato
This is where the whole intent thing can get tricky. One of the insane things I do is I seek out the cleanest copies of out-of-print CDs of titles I want. The problem is that used CDs not as described a lot, and when buying from certain marketplaces, you have to return the item on your dime in case of a dispute. I've lately been buying Japanese CDs, from Japan -- too expensive to return, and too expensive to buy and have shipped one by one. So I would buy a few copies of the same title and have them shipped together. Then I pick out good copies and list the ones that don't meet my standards for sale. The intent surely isn't to re-sell for profit; the intent is to buy a few good copies for my personal collection and personal use and let go of the bad apples because I have no use for them and recuperate as much as I can (because each CD adds to shipping cost, plus there's handling for the guy in Japan who accepts all CDs from disparate sellers and then sends them all to me in a single package).
And another situation is where I have a less-than-ideal copy from earlier, "upgrade" it by buying a better one, and then once the "upgrade" arrives, sell the old one.
Where would I even begin explaining the intent to HMRC? I know this is not a normal scenario on this planet, but it's not an imaginary one. And the impact of that on my bank account has prompted me to sell off even some of the copies that I bought as "upgrades" (which even further make it look like a flip-job).
Maybe the key ingredient here is that the intent is to buy good copies for personal use, but due to how the used CD thing works, I know that some will be in inferior condition to what I'm lead to believe by the seller, that is not fit for [my] purpose, and I'm prepared to deal with that by selling the bad ones. Sort of like what I see on Guitar forums: people take a chance on guitar sold on eBay and go into it "it's just 1,500 quid -- if it's not good, I'll sell it". Instead, a CD doesn't cost 1,500 quid, so I buy them in greater quantities... So I wonder what HMRC would think about that....
I would say they would consider your intent is to trade, you just don't know specifically which items your buying will be to trade on and which are for your benefit.
Bear in mind your only going to be taxed on profits. So if you imported £10k of used CDs and then sold £9k worth which you can fairly say cost £9k there is no tax due. Just some minor reporting of purchase and sale.