yes, I was upgraded to biz class on airtran without even offering a tip. I asked the gate agent how much to upgrade, and whether I could based on my fare. I think I had a discount fare, and you could upgrade to biz from a full price fare for $25. She upgraded me and never asked for anything. I didn't tip her either. This is not relevant to the OP, but is relevant to people who say its impossible for the FA or GA to do this. I'm sure there are FA's who would upgrade you for a discrete $50 if they thought the chances of getting caught were low, and this is probably even more likely in other countries. But note tipping and being allowed to sit up front is very different from having a guaranteed upgrade wtih meal, etc. The main difference is once the plane pulls away, the airline has lost the revenue opportunity.