7) If he has no reputation (including most cases when he is a newbie or a Jr.), even small tranches are a risk. Better use an escrow system, like the one of bitmit.net, or a trusted member, or you might need to send over 10 very small tranches. It can be annoying, but loosing your money will be more.
8] For big amounts always use an escrow system, unless the member has an excellent reputation.

Since this thread is a sticky, I decided to post this here. Any moderator or member feel free to move, copy or improve these rules at will.