Advice please? The difference between a 'dealer' and a 'trader'

We have just put a deposit down on a used Toyota Yaris. We thought this was a private sale (via G******) and looked at the car on the seller's private house driveway. But when we have come to sort out the collection details for car tax the seller told us he runs a paint-spraying company and has been using the car as a temporary customers' car and has also running to and from work in it himself for the past 4 months - yet he is not registered as keeper. When he fills in the log-book he has told us he will fill in the yellow section as a 'trader/dealer' not as the keeper. As far as we could see on the logbook the keeper is still registered to the car's original owner.

So, my question is should he be selling the car as a 'private seller' as per the ad, or as a 'trader' having loaned the car out to various customers during his 'ownership' depite not actually being the registered owner? (Is it legit to loan a car out without being the oregistered owner/keeper? Who would be liabel for any speeding or parking fines during this time?)

And are our consumer rights any different if he sells the car as a private seller or as a trader?

We have looked up online and can find no defintive description for what quantifies a 'trader' or a 'dealer' and want to know what's what before we pay the balance! From the seller's side what benefits are there to the way he is trying to do things - is it legal? He seems like a decent guy but we are totally confused and clueless!

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