if a web app. id have escrow built into it as standard. so that one person cant then make 100 clones and rate his other 99 names without showing a valid trade has taken place.
i personally do not take the otc rating onboard as my guide of trust.
there is in the UK a service called
bitbargain.co.uk that has a built in escrow and shows exactly how many trades of actual coins a person has done, how many times the deal has been cancelled and how often the person did not respond.
this to me is a far better and trusted system, not only because of escrow, but because the rating is not just based on someones response. but based on actual trade information