Okay, I can kind of get the legal concept of why TER has to have this De-Listing procedure available to providers upon their request.
Still, there would seem to be some compromise options that would be of tremendous benefit to TER members and that would not cause undue legal exposure.
My thought is simply that TER have a reference of phone numbers and email addresses of providers that have chosen to delist. When a member does a search, it pops back with a simple statement: " Delisted".
Where is the legal exposure on that??
It could even be a benefit of VIP membership, only available to VIPs.

(I sure hope you moderators don't censor me on this!!)

Along with the above, the database of delisted providers could be used as a checksum to prevent them from delisting because of a bad rap and trying a return to get a clean history.

Of course, I assume you do not do that already, and you probably do it already, but in case you dont....(end ramble.)