Selling on Ebay to be monitored by the Taxman.

How can they do this though.

ebay have recently sent out this message about tax etc.
www.ebay.co.uk/sellercentre/selling/selling-online-and-hmrc?mkpid=2&emsid=e99011.m2.l1&bu=43097300677&osub=81946554bc1e89fc32dce19921d6c3c6%257E1710833894548EM_T_ALL_T&segname=1710833894548EM_T_ALL_T_GC_3_20240327_8005_26100986_26100915&crd=20240327020147&ch=osgood
No mention of benefits and how ebay sales might affect that, just tax.
According to ebay the must inform the govt. if you have more than 30 sales on ebay.
But no tax to pay unless your PROFIT is above £6000.
I know for benefits purposes £1000 of profits is disregarded. But anything over that that is deemed to be profits, ie bought for less sold for more deliberately, ie trading will undoubtably come off your benefits.
But here's the rub. How is anyone going to prove that you were trading ?
If I buy something for my own use and then decide not to keep it and sell for maybe a bit more, maybe a bit less than I paid is that trading ?
It's difficult to prove.