It would make sense for crossings to be intentionally different besides the agents personality. Not knowing what to expect gives the agent the upper hand in evaluating your intentions.
And sometimes the agents don't get it: Arriving via ferry in Victoria I was buzzed through in the MH. DW in the toad (with towing baseplate) was quizzed for 30 minutes. No hotel reservations, no luggage, 3 weeks planned stay and repeat, repeat, repeat. She kept saying my husband is in the motorhome that just went through with my clothes and we're going to campgrounds...
We laugh about that experience.
Another time we got on the ferry at Victoria and went to the deck where we observed many agents carrying armloads of alcohol from a MH that just arrived. I'm sure the owner was not a happy camper!