This is a persistent issue that will not be solved unless there is a required onboarding for users before they could interact fully with iNaturalist. No amount of commenting “@username I think this observation is of a [captive/cultivated/captured and kept/etc.] [type of organism]. I went to the Data Quality Assessment of this observation and marked this observation as not wild for the sake of preserving the quality of data. Please follow up if this [type of organism] is actually wild." and directly messaging them about the situation is going to make them stop.
I have long been a proponent of discarding the idea that iNaturalist should be a place for tracking one’s engagement with nature. If that was the main mission, we will inevitably have people not caring about quality at all and not bothering to do their due diligence to improve their observation skills (making a preliminary ID before posting, narrowing down the positional accuracy, making sure their dates are correct, adding annotations, adding observation fields, adding to projects, and filling out the DQA when it is needed). People can just save evidence files to their device(s), update the metadata, and add them to sub-directories in their file system without needing to post anything to the public.
Since onboarding feature requests are not up for consideration, this “reminder” cannot be done, and identifiers must remind people to mark the wildness of their observations and take time out of other tasks to do this.