I tried this once to upgrade my room to a suite, you basically put $20 in between your ID and credit card when you check in, and ask if there are any complimentary room/food/credit upgrades with a smile.

However, I was with a coworker who knew the 2nd-in-command boss of the hotel. So one night I was having fine dining with them and got pretty drunk on the free wine that was served to me. I accidentally spilled to the boss that I got upgraded to a suite just by tipping the front desk person, he got pretty furious about it and I think I cost that front desk person his job :/