I don’t exactly hate those people myself. It's more that I'm afraid of how they might react to me when/if they find out I'm on the "other" side. They are constantly told all kinds of lies about those of us who oppose Trump: that we are all "radical" communists or socialists (or both -- they don't know the difference, of course), that we "hate this country," that we have an aversion to Trump only because we have "Trump Derangement Syndrome," and on and on. Knowing all that makes me a little more distrustful than I would be otherwise.
Whenever I have a pleasant interaction with a stranger who "seems" nice, I try to take it at face value and appreciate it for what it is. If there's a question in the back of my mind, as to whether they would be this nice to me if they knew I voted for Biden/Harris and for Harris/Walz, I try to ignore it. In some ways, I'd rather not know. If I was aware that they voted for things that I find repugnant and destructive and inhumane, I know it would affect my reaction to them, so I just choose to put on blinders and put that kind of stuff out of my mind and just respond to how they are behaving in that moment.
But I'm talking about incidents where I know I'm not likely to ever run into that person again. If I encountered someone multiple times as you described and was likely to see again, I'd definitely start wondering. I'd cautiously feel things out and try to get a sense of where they stood before getting too invested. And if I did find out for sure that they were a Trumper, I'd probably back off a little. I'd continue to be pleasant, but my guard would go up, at least a little.
I hope this guy ends up surprising you, Aristus, by turning out to be someone who is truly as nice as he seems. Who knows, maybe he took that job because it happened to be in a good location for him or because it had the kind of hours he wanted, or some other reason other than his being deeply invested in their belief system. Stranger things have happened.
For what it's worth, my husband is an old guy with gray hair and a beard, who looks like he'd be right at home at a Trump rally, but nothing could be farther from the truth. You just never know! 
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