How do you know if your oppenent is significantly better than yourself? Rule of thumb, if you've been around for less than a year and your opponent is an NPC, you're a carcass waiting to happen. If your opponent is a PC, older than you and combat oriented, you're in the same knackers yard. Otherwise, take your chances.
As a rule of thumb tho, -usually- if your first flee fails, further attempts are a waste of time. 'posture guarded' and see what happens. Every time you -try- to flee you lose an attack so repeated attempts not only achieve nothing but minimalize any hope you have of winning the fight. Guarded gives you the maximum chance of blocking attacks against you with the added bonus of counter-attacks, which are actually your best chance of hitting a superior opponent.
You know, I'm going to start a site to give all the insider secrets of Sindome and how best to rape the system ;)