Should I be worried if I found one cockroach?
As a general rule, yes. Seeing one cockroach is more like just the tip of the iceberg. Our experience is that if you see one, then there are quite a few more, and these roaches are excellent at hiding and breeding. It is much better to nip that problem in the bud and start a treatment program to eradicate the pest before their numbers become too large and they are much harder to control.