The same now, there’s no way of recording trade movements with the DVLA after initially being put into trade.
Record keeping is key here.
If it’s a trader unknown to you I strongly suggest you also get a copy of photographic ID or photo their truck/trade plates etc. Over the years I’ve only had a few of these trade deals that turned slightly sour when 6 months later the police drop-in unannounced or a speeding fine dropped through the letterbox. However police investigations etc. are NOT my concern, making money on cars is so as long as I’ve got some basic form of I.D. that’s good enough for me and, more importantly, good enough for the authorities.
There’s too much worrying here about who you sell too. If someone says they’re trade then they’re trade, however flimsy (or non existent!) their proof.