Fiber is indigestible and does not affect ketosis. That is why many companies only list their net carbs (which as someone else pointed out, is total carbs (gross) minus fibre). Net carbs show you digestible carbs, if that makes sense. Fiber just goes right through you, which is why people mix those fiber supplements into their drinks. That is also why certain green vegetables (which contain a lot of fiber) do not affect keto. It sounds like this Exante rep doesn't even know what he or she is talking about.
If anyone wants further reading on this, it is almost always talked about on Atkins forums and in Atkins articles.
So the answer is, look at the net carbs and keep track of how many you are consuming throughout your day. Bars have some, water flavourings have some, etc etc. I believe Atkins advises no more than 30g digestible carbs per day to stay in keto, but you should check that.
Again, if a product lists total carbs (also known as gross carbs) but not 'net carbs', then you can figure it out for yourself by taking the total number of grams of carbs, and subtracting the grams of fiber.