This question is addressed in the FAQ: What should I do about “duplicate” Observations?
In short, duplicates are indeed annoying, but the best coarse of action is to leave a polite comment and move on.
My go-to copy and paste is:
Is this the same individual as [this observation](link here)? If so, please combine all photos into a single observation. There are tips for combing your observations here: how to turn multiple observations into a single observation. If this is a different individual, then separate observations as you have them is fine.
I adjust some of the wording if it is clearly the same individual, such as the same photo being used for both observations.
Some of the wording here is ambiguous, so I’m uncertain if you are referring to observations of the same individual over multiple visits/days or multiple observations of the same individual on the same day. The former is a valid procedure, and the latter is not. From the FAQ’s What is an observation?:
if you take multiple pictures of the same organism during the same encounter, please combine them into a single observation. If you revisit that organism later […] you should make a separate observation because it was observed on a different date.
As a note, iNat data doesn’t equate to and shouldn’t be translated as abundance data.