Selling the coin to someone you have not met and the person paying money to someone he too has not met in trust is another dimension of trust. In all Bitcoin is built on trust though ,there are those that will want to cheat.
If you knew how the basic market system operates, you would easily understand how bitcoin works and bothers little about the buyers and sellers being complete strangers that have never seen themselves before. the trust that allows for such transaction is not based on the individual involved but on the system that both parties are operating under.
p2P that you carry on through an exchange has it own issues so you sure have to also exercise your own level of carefulness so you do not just talk about the trust you have on bitcoin while taking out the fact that some of the strangers you meet while doing your p2p are scammers that are constantly trying to outsmart the technicality of bitcoin and exchanges that are used in carrying out p2p transaction. bitcoin is worth every hype but still, put things in the right perspective so you don't become too vulnerable to scavengers.