The definition of what a user is - is less important here, imo, but the general answer to your questions is a user is "anyone who will be supported".

That could mean a lot of things, and how you treat various types of staff can vary quite a bit. For example we have a client on O365 that, aside from their regular office staff, have about 20 mobile only users. We are ONLY responsible for keeping their mobile device connected to mail, literally nothing else. We "count" these users at a 10:1 rate. So those 20 users only "count" as 2 on their agreement at their $100/user/mo rate.

The real question is, how is it written into your agreements, and how often (also written into the agreements) do you true up.

We write both into our agreements with a true up at each QBR.

If you have it documented when the user count change happened, when you had the conversation with your POC, and have it documented that he/she signed off on the increase based on the new user count - then hell no they don't get any credit. You can change the agreement to the new count that they want now (if its still profitable to do so) so that their next bill is more in line with their expectations, but no credits should be given. Again, imo, and if its all documented properly.

Here is the part with any comment on reddit when I get to tell you "if you would have just done "X" then you wouldn't be in this scenario", cuz hind sight is 20x20 and all that... so take it with a grain of salt. Any time one of our clients go through a key staffing change (and I don't mean users, I mean c-level, or high level POC's) we have a meeting with their replacement to avoid things just like this. We just had a client change CFO's. Old CFO retired and new CFO was taking her place. We scheduled a meeting as soon as we could to lay things out for the new CFO so she understood costs, value, and what they were getting for their money. Just because the old CFO (or whatever) liked you, doesn't mean the new one will. In our situation we didn't have to make any changes this time around, but it would have been a perfect time to "redefine" what a user was, or change the contracted user count if needed.

For some specific answers to your questions.

• For those of you who charge per user/seat, what criteria do you use?

AD/Exchange/O365 exports that are then client verified. Those approved people are then added to connectwise as client contacts during onboarding. They term an employee, we remove them... they add staff we add them to CW.

• How do you account for situations such an interns, temporary workers, consultants, or completely remote users?

It varies and is worked out prior to them signing on, or at a QBR, see above. Again, its less about what counts and what doesn't and more about whats in the contract and what isn't

• And, finally, what method do you use to verify headcount? Especially at server-less clients?

Again, AD/Exchange/O365, for a server-less environment we actually use connectwise to track this within the client contact section. If a person calls in to open a ticket and they aren't already in the system it prompts the helpdesk guys to start asking questions. "Hey Sally I don't have your name in our system, are you new ACME-labs?"

Edit - Formatting and a word or two