user6: What mechanisms does OTC web of trust have against someone creating several accounts and trading between with themselves over a period of time, giving each other perfect ratings. 

user403: The global ratings are fairly easy to manipulate as you describe, and it has been done before. There is some minor protection provided by the requirement that you need a positive OTC rating to rate anyone else.
#bitcoin-otc also supports "trust rating" (example) which can't be easily manipulated.

6: <p>What mechanisms does <a href="http://wiki.bitcoin-otc.com/wiki/OTC_Rating_System" rel="nofollow">OTC web of trust</a> have against someone creating several accounts and trading between with themselves over a period of time, giving each other perfect ratings. </p>
 403: <p>The global ratings are fairly easy to manipulate as you describe, and it has been done before. There is some minor protection provided by the requirement that you need a positive OTC rating to rate anyone else.</p>

<p>#bitcoin-otc also supports "trust rating" (<a href="http://serajewelks.bitcoin-otc.com/trustgraph.php?source=theymos&amp;dest=Keefe" rel="nofollow">example</a>) which can't be easily manipulated.</p>
