... not being able to post somewhat exact locations makes it hard to share information on identifying species that one observes in the field.
There will always be the problem of providing good information for scientific purposes and responsible people without opening it up for irresponsible commercial collectors. I think the best we can hope for as a compromise is to use sound judgement in presenting locations. Be generalized in public postings, and if someone responsible needs more details they can communicate through non-public channels. For most purposes on this board very generalized information is adequate - such as "southern Arizona" or "near Rio Rico". Even with this, a determined commercial collector will figure out some of the specific collecting sites, so consider that in postings.
While the concept of keeping specific collecting information quiet is a good one, I'm not sure I'd want to see a formal set of rules put into effect. Such a set of rules would either have to have a lot of flexibility or would need exceptions and variations written into them, making them too rigid or too cumbersome. As a community I think we can influence each other to use good judgement - and moderators can step in if they perceive a posting that endangers a population.