As I see it there are 3 parties involved in the transaction: the user, the OP and the RP. There is some trust/risk factor associated with each relationship.
From the user's perspective they "trust" the OP (either because they want to spam and so are using an OP that makes "false assertions", or because they trust the OP to protect their authentication credentials and represent them correctly on the web). The user may or may not trust the RP, but by logging in they are making some level of trust/risk assessment.
From the OP's perspective the user represents some risk/value metric (too many "bad" users and the OP gets blacklisted). The OP protects that risk by potentially verifying email or cell number, supporting PAPE and other strong authentication methods, etc. The OP also has a risk/value metric with the RP though this is probably not super important right now. I can envision a smart OP warning me about authenticating to an RP that it some how determined is not "trustworthy".
From the RP's perspective, they have a risk/value metric on the user (e.g. Is the user going to be a good citizen of my community? Are they going to abuse the resources I provide? How much effort do I want to put into detecting "bad apples"?). The RP also has a risk/value metric on the OP (e.g. When the OP says they support the PAPE extension do they really do it?). Finally the RP has a risk/value metric on the resource/service they provide. From a business perspective I don't believe it's wise to blatantly "trust" the user if the resource/service is highly valuable (e.g. moving funds between accounts). Most users today don't have the sophistication to make good decisions.
Ok, so maybe I was a little unfair in my characterization of “most users”. I was trying to say that I don't believe many users know how to chose a good OP. In fact many will just use an OP they already have (which puts pressure on those OPs to be good citizens; that's a “good thing”). So, if an RP has a high trust metric with the user's OP, then they can more confidently trust the user as well. On the RP side its really an assessment of risk against the “User:OP“ pair.