I'd take him with a pinch of salt.

[beachboy]

Longman Language Activator mentions the idioms to look upon/view/regard somebody with suspicion. Do they do the trick?

1 - If I were you, I'd view Jim with suspicion.
2 - There's something mysterious about this new employee. I view him with suspicion.

Do the sentences above sound more natural?

[tedmc]

Reservations about certain people, like gut feelings, comes from within yourself based on previous experience. You cannot be told about them.

[jutfrank]

I don't like sentence 1 and I don't think it works. It's not normal to advise somebody else what view they should have. The phrases you're using (having reservations, viewing someone with suspicion) are used to describe the impressions we have about something. You can't tell people what impressions they should have, because impressions can only come naturally.

Sentence 2 is okay.

[cross-posted with tedmc]

[beachboy]

That's what I thought. In Brazil we have an idiom that works in both sentences in post 11, but I don't think I'll be able to find one in English.