Dear Mary: How should I handle summer invitations when I might get a better offer?

Q. In order to raise money for a worthwhile cause, I have agreed to open my garden for the first time and provide a sit-down lunch for 30. My problem is that there are certain local people who I really don’t want to come and snoop around, but I fear that once they see the advertisement they will be the first to buy tickets and thereby displace slower-off-the mark locals whose company I would genuinely enjoy.