In my eyes, spamming is considered when a user sends you pm multiple times with same issue.
If someone sends you one time pm to inform you something, then it is more likely a promotion.
Lets say, you have a famous blog and in your blog you have contact us system.
So if I contact you to make a article about our product/service in exchange of money/coin/token, will it be considered as spam?
I have some facebook groups, and I do receive msgs from companies sometimes to make pin post.
But I don't consider that as spam instead I consider as inquiry.
But if you have zero tolerance then you can do two things, either put them in your ignore list or report them to admin.
This is actually the best way to understand this .
Maybe it is "spamming" or maybe it is "promoting" . With spamming as mentioned is the repeteion of the same message by the same user . But if the manager is sending some pm explaining the need and value of the bountie that might just be considered as "promotion" or "marketing" which is what pretty much evry body is doing in the forum . Its up to you to decide what that actually is .
If you think it is spamming , there is always an option of reporting . But i really don't think that some managers would take such risks of getting reported and getting negative trust.
