Imagine being tired from a delayed flight getting ready to check in at a hotel while you are hungry, and you answer the opening question "How are you?" from the hotel team member with "Ugh! It's been a terrible day and I cannot believe how ridiculous travel is!" versus saying "It's great to be here! Hope your day has been a good one!". The person behind the desk has likely been ignored, treated poorly and treated well during the day. It costs you nothing to be positive.
Now, onto the upbeatedness of this: Think about asking that person what his favorite rooms are, and if any of those are available, adding you are not in a rush to wait for something s/he deems to be special. Often, showing that upbeat approach, and being genuinely interested in the other person, you'll get upgraded - not because you demanded it, had points for it, or paid for it, simply because you upbeated your way to it!