The technician will assess the activity in the baits over the course of the program and, usually, make a judgement call as to when success has been achieved (the subterranean termites killed). A good tech will almost never tell you that the termites are all gone but will talk about colony elimination or control or the length of time since any of the bait has been eaten. You’ll still need ongoing inspections as baiting provides no residual control. Often colony decline can be observed to be happening when the proportion of soldiers increases or when the feeding workers develop white abdomens (uric acid crystals).
Baiting is used for subterranean termites (not drywoods and rarely for dampwoods). Baits use slow-acting toxins in low doses. The big problem is that there may be more than one colony active in the area Some colonies have fuzzy boundaries so that outside termites may be recruited to replace those affected. A great example of this is from Devon, England where introduced termites turned up in two houses. More than a decade of baiting later, there were still some termites active.