When there's a bit of moisture in the sky, it will lead to "Flaming Star conditions", as I like to call it: halos surrounding brighter stars that all try to mimic IC405.

Dew on the optics and breathing on an eyepiece will do the same, but that will be obvious much quicker.

For Sazhen 30 there will be little trouble to differentiate between a faint reflection nebula surrounding a star and a false neb. It's in a pretty rich star field with plenty of stars of comparable magnitude nearby. If there's only one star revealing nebulosity, you can be sure that's it not a false positive.