Verifying identity for clients could be a way to avoid scams. Or at least this should be an option for clients, for sure it will attract better biders for their projects.
If you mean "verified payments" feature then it is already there. I guess it is reasonable to not make the clients jump through all the extra loops when he signs up but it will be great to make more statistics available to freelancers like number of disputes made by clients and refunds made to client profiles so that we can better filter out the bad ones.
Yeah, number of disputes made by clients and refunds made to client features would be much appreciated. I always spend time to find out those values manually. Some time without any success. I guess oDesk can provide those features. This will also make the clients responsible for refunds. Thus better work will be produced from the platform.