Takes 5 minutes to find a good write up and copy/paste into a new advert...
I have dealt with gumtree through my line of work and a truly incredible amount of crime takes place on there in relation to car sales!
A common theme goes a little like this...
Buyer finds a deal almost too good to be true and arranges to meet seller at sellers chosen location, buyer arrives at scene and meets seller....and sellers friends, buyers money and most likely the car he is traveling in drive off into the sunset!
However if you really want to take your chances follow the advice posted above but also arrange to meet at the local police station car park.
Good luck!