“We really love the young couple who are buying our home and want to leave them a gift. What’s the normal etiquette for this? Do you think it’s a good idea?”
First of all, how nice you are to be so thoughtful.
This is relatively uncommon, so there’s no accepted etiquette. You can give them a bottle of wine, flowers, or whatever you feel is appropriate. And you can leave it in the house or give it to them in person.
Do I think it’s a good idea?
Yes, for two reasons.
The first is that it’s just a nice thing to do!
The second is more practical. It’s always good to have warm, friendly feelings in a sale, just in case things go sideways during escrow or after closing. It just makes the resolution so much easier when both sides like each other.