To be sure, due to the different fighting methods of the guilds, going one on one in declared, prepared combat is not suitable for those who use stealth and surprise as one of their methods. I personally have no problem with that. From the sounds of it, your methods are similar to mine, a more workable system: Go for the kill, and leave it at that - or use other methods to do far more lasting and hurtful damage (usually in the wallet!). It all depends upon whether your opponant works in similar ways, i. e. with respect.
Personally, I feel the bloodlust/challenge system is fine in theory, dodgy in practise. If all you ever do is defend, yet are attacked by combat-happy fighters (who don't challenge) then you will get bloodlust regardless of whether you challenge them or not (if you win of course). Since they fight so much, they are liable to get killed on challenge regularly, and thus keep bloodlust low. You on the other hand, get a rising bloodlust; This can then by exploited by the unscrupulous - team up, completely cripple the defender, and then challenge them. Slay them while they are helpless, and bingo, the hapless guy, who never attacks, only ever tries to save his own life - loses large numbers of shiprides and lots of xp. In fact he gets the exact same 'punishment' that say, a mass-murderer, with high bloodlust gets when he is finally brought down by a righteous