Before, you would not had blue tick on something that looks like major brand, known person etc. So yes, quite often you could know "this was said by this person".

The trolling (both for fun and for harm) on platform went off the charts last two weeks and there are multiple blue checkmarks accounts for a lot of companies/individuals.

Sure, to the extent you could trust any other piece of writing. Tweets come with the same caveats as any other source of information and require critical thinking to process.