Very briefly. I’ve had this answered before but would like more opinions.
If an authentic and original spirit sigil is opened and charged by calling the spirit, I understand the spirit and possibly their legions will come but can a random parasite also come through that you did not call?
Or is the sigil a strict link between you and only that specific spirit until the sigil is burned or buried?
Yea he answered that actually 
I’m seeing what others think.
There was a reason behind the kind of preparations you see in the old grimoires. Two types of cleansing always took place. There was the cleansing of the magician as well as cleansing of the ritual space prior to doing the work. Even that was preceded with a several days of mental preparations. Hardly anyone does any of that anymore and so now you hear all of this talk of parasites and imposters. No wonder.