TER General Board
It's a legitimate claim after one review, even a negative one. I think that...
Well, the obvious answer to your question would be one (1). If a provider has a review on TER, they could accurately claim that they are TER reviewed.
But if you are asking about a provider advertising with a "TER Reviewed Site" logo on her web site, the answer is none - no reviews are required to make that claim.
See the links below for the requirements for getting a site TER reviewed:
http://www.theeroticreview.com/site_reviews/index.asp
http://www.theeroticreview.com/info_policies/siteListingHelp.asp
http://www.theeroticreview.com/discussion_boards/viewmsg.asp?BoardID=33&MessageID=10088