I am not sure if this has been suggested and I know that combating RMT is tricky business, however I don't think SE needs to do it alone.

I suggest giving us an interface to set up our own tell blockers which can help combat RMT as well as harassment.

Simply give us a window that we can input phrases that we commonly see in RMT tells such as "real" ".com" those [ brackets no one else uses, and other tricks that are not common in every day chat.

Once those are set up and a tell happens we can be notified via a system message that a tell was blocked and give the name of the sender so we could identify if a tell was wrongfully blocked. A log could also be kept if we want to go back and check to ensure real tell did not get blocked by mistake. These reports could also be used by SE to flesh out their own RMT filters.

Something along this line I think would be helpful to the community by lowering frustrations with these tells and also reducing feedback to the gil sellers.