The amount of (if any) pest hitchhikers you get is a matter of chance and can vary depending on the specific shapes you receive as well as the amount in weight. I have received 3 seperate shipments of TBS rock in the past several months and got 2 mantis shrimps in the first shipment and none in the following 2 shipments. I also received a handfull of crabs which I have since caught and removed.
I believe many of these bad hitchhiker threads are overstated and not as bad as some people make out, and certainly not a valid reason to avoid buying TBS rock in my opinion. Many of the bad guys can be removed from the rocks upon arrival, and the rest that may or may not turn up can subsequently be captured and removed.
The grim alternative is buying live rock from overseas which has virtually no life whatsoever other than some dead rotting plant material and a few patches of coralline algae that survived the scrubbings and curings and wrapped in newspaper for days on end and sitting in airports and warehouses and everything else. And the stuff at the local fish stores in my experience is even worse, and usually looks like rocks I would find laying in my back yard.
