I currently have trust depth 4 because it gives me a higher trust rating. At depth 4 it shows 4: -0 / +6(6) if I set it to depth 2 it shows 0: -0 / +0(0).
Not sure why it displays a 0 score when I use depth 2 while I have completed plenty of trades.
It does not matter what it shows you, it matters what others see. Six or even four is a very deep trust list, like trusting friends of friends of friends of friends.
HERE is a good discussion of the problems with default trust.
This thread was started by theymos himself to try and figure out what to replace default trust with.
Good luck and welcome!