Kelley, I treat new trees/plants coming in with horticulture oil IF I see pests( the soil as well), always keep them separately from other plants for a week or two and after that they are fine.

Thanks, Sunshine! Stupid question: do you water with the HO mix or spray the top layer of soil?

Just spray the top of the soil. Sometimes if I see white salt residue on top of the soil, I remove it gently and add fresh soil.

You are not overreacting, it is good to be cautious. For new plants I start with a strong water spray, then after drying, some sort of spray, usually soap, but HO would be anther top pick. Even with careful inspection, you may not see the pests.

If the rootball seems like it will slip out of the pot, I like to pull it out to at least take a look at the outside of it. You may find root mealies or other pests, or rotted roots. You also risk disturbing the roots, so it's a judgement call. Then lightly water it in, and do the above mentioned spraying.