Hopefully this advice may be of some use.
As a counter of some experience, could I recommend that you smile and be polite to the counters - they are genuinely trying to do their job. By all means point out errors, but in a constructive way. I in no way think you would be critical, but in my experience, some agents can be very abrasive and actually distract staff from the task in hand. Also, don't be surprised if the counters don't talk to you, or even acknowledge you overtly. They are not being rude - they are following instructions. Guidance varies, and different returning officers handle it in different ways, but in general counters are instructed not to respond to anything other than simple informational questions - which polling station are you counting? - that sort of thing. If you have questions about process etc. - find the returning officer, a depute, or a communications officer (should they have one) - the count staff are there to do counting.
Counts tend to be on quite a tight schedule - there is a pre-booked slot they they are supposed to hit in terms of confirming the count, so the count staff are under a bit of pressure, particularly early in the process, to get things counted ASAP. You never know when you might have to recount or get a lot of papers going to adjudication, which can really slow things down later on.