berry120 (and the Site Team) -- thanks for the response.
One way to spot it is to look at past posts. Some of the shills got 100+ post counts, so they are easy to spot. They would vouch for a different post per post, yet seem to still be on the hunt of good host (for other shills to reply to their requests).
WHT's method of preventing this is to ask for proof of use for all forms of review. This is a good method so far, but they have a huge team, with a user base very good at spotting this sort of thing. Reviews include a length of use, which is good for readers to evaluate how worthwhile the review is by its own merit. These shills have been shilling for hosts in the count of hundreds. I doubt they will be able to provide proof of having purchased accounts from all these hosts.