Airline upgrades are almost exclusively done by formula, with little discretion allowed to gate or check-in counter agents.
The only time there may be wiggle room is when a flight is oversold, and while elite frequent flyers may get preference for moving up to a premium cabin, the most important priority is getting a flight out on time. Other than these “operational upgrades” though, upgrades are going to be based on published criteria – not who is nicest, who dresses best, or who asks.