I have been one of those "gate keepers" (read: receptionists).
In the beginning I tried to be pleasant to salespeople. After the 25th call from a telemarketer it gets irritating. If the phone call just takes 1 min. I have already wasted 1/2 hour of work time for the day.
Soon after I would just say, "We are not interested, please do not call here again," and hang up.
If I sounded bitchy, it is because I am trying to do my job and don't want to get interrupted by a stranger on the phone trying to sell me something we don't need. I had one woman from a temp agency, who would call every single day.
She found out who else worked there and try to get through to them. Finally, I had enough, I cursed her out and told her even if we considered needing a temp worker we would not call her agency, because of her actions.
Never heard from her again. My boss could hear me and just laughed.