A few years back I sold a personal possession on ebay when I upgraded and happened to make a decent profit so I started to look for similar items (nothing to do with airguns) that I could renovate, repair or break for spares and sell on. I would describe it as a hobby that paid for itself but no doubt about it, it intentionally made a profit. Nothing huge but not always mere pin money. About 2 or 3 years ago I got a letter from HMRC that said that it looked as if I was an on line trader and I needed to submit a tax return. Now, I had bought stuff over the years that ended up being scrapped or sold on at a loss as well as bits I had done well on. I had no records other than bank statements, credit card statements, paypal and ebay records and I had no idea what HMRC knew or how far they would look back. The honest truth is that I had no idea how much I had made, and no way of writing off losses against profits. I couldn't trace many legitimate expenses as I often paid cash and kept no records.
All a bit naive on my part.
It caused no end of sleepless nights worrying about it. I ended up collating everything I could trace, going back as far as I could, and paying a tax accountant to do the return for me and setting things straight with the revenue. I ended up owing the accountant four times more than the taxman.
The stress it caused me more than cancelled out any profit I had made, and the truth is, I don't need the money and I really only did it because I enjoyed it.
The parties involved are now quite open about this, ebay will tell you how much you can sell before they are obliged to tell the tax man and the tax man will tell you how much you can make before there is any obligation to file a tax return. Stay bellow these limits and all will be fine. There is not neccassarily any tax due just because you sell over these limits. Selling your outgrown baby clothes, the bicycle you no longer use, your old vynyl records and collection of limited edition Daystates won't neccassarily attract a tax liability but if you look like you are dealing, you may be told to file a return.
Being an enthusiast that changes his airguns every week
may make you look like a dealer and you may have to show that it's simpy a hobby.
If you are buying to sell and make a profit over the allowance, then it's a business and it's only right you pay what's due.