ALWAYS buy the seller. ALWAYS ask for people's opinions on a certain person. If someone can vouch for that person, that's even better. People who are in the watch 'game' or heavily into the watch community value their Brand name more than a few thousand bucks.
I started off as a newbie and still am. But I do everything to make sure that I build up my Brand name. I make connections with the JLC Boutique, when I sell my watches I provide more than sufficient information on how I purchased the watch and why I'm selling, heck I even gave the person whom I sold my watch to the invoice of purchase (has my address and tells how much I purchased the watch for). A little overkill.... but these are the lengths I'm willing to take to ensure that people trust me.
Trust works both ways as well.
Adam