Hi, no you do not have a need to register it. There is no way of knowing if it is stolen. You will have to go with your gut instinct.
There are no registration docs but if the current owner has any purchase receipts etc and instructions then this should be in your favour.
You can't really tell, the current seller might be genuine but I suppose it could have been stolen when he bought it. The way forward is to buy it at seller's home address & don't do anything silly like arrange to meet seller at motorway services for example.
If you're worried, get a friend to drive you, ours dropped us at the address and drove round the corner, once safe we text her and she brought the money
------------- As a child my families menu consisted of two choices: take it or leave it.