MinimumRest I don't even know what our company policy is on this, and as my countrymen are not known for their free-spending ways, it's not a problem that often arises.
But sometimes it does. I tell the pax that I very much appreciate the gesture, thank them for their intended kindness and politely and with a big smile refuse to take any money or gift from the tax-free trolley.
Only exeption is for the elderly who at the end of the flight take my hand, utter something like "lovely flight my dear, thank you so much for looking after us so well" and then with an air of great secrecy put a coin in my hand.
I thank them profusely in a conspiratory whisper, and make a bit of a show of putting away the coin safely.
IMHO they stem from an era where offering a tip to staff was the most practical and welcome way to show appreciation for a job well done. They mean well, and in their value system it is perfectly polite and not demeaning at all.
To me, refusing a tip offered in that particular spirit would feel churlish.
Hope this helps.
.....Oh and aluminum...... in case you start wondering, last time someone checked I appeared to be of sound mind.........or was that simple? 