Sentence Correction

Can someone please explain the difference between a modifier that modifies the preceding subject and one that modifies the preceding clause ??

e.g. 1 ) while depressed property values can hurt large landowners, they are potentially devastating...

-> couldnt 'they' refer to landowners or property values ??

e.g. 2 consumers may not think of household cleaning products as harmful substances, but many of them can be harmful to heath...

-> if I take the meaning into context this sentence makes sense...but if I think about it from the subject-pronoun placement point of view...'them' could refer to consumers - based on question 1's logic above

Any general wisdom on this topic ?

Your question is regarding pronoun ambiguity.

In the sentence, "while depressed property values can hurt large landowners, they are potentially devastating..."

they refers to property values not landowners. Anything you get this problem, simply replace the pronoun with each of the noun it seems to refer to and see if only 1 makes sense. if that's the case, then its fine.

in this one, landowners cant be potentially devastating, so "they" refers to property values.

Clear?