HUGS, Carla. I've had days like that.
I immediately outlined what to do in the future.
...One thing you can do is state that you have a policy for what you give. And sweetly but firmly offer a product or service. Don't say "Can I offer you..." because you don't need permission to ask for money for your work. You can also state that a worker is worth their wage, and a gift isn't an indication that your work is free.
If you have several free gifts being offered through different channels, you might put together a page where they can get to all of them with a password, and have that go out in an automated email.
As for security, just have your security certificate ready and be willing to talk to your developer, the company that certifies your site, and the company that runs your cart. Then report back with your findings. The more third-party proof you give, the more likely they are to listen.
Unfortunately, usually once someone has something like that in their head you can't convince them otherwise. So once you've done everything you can, pray for them, forgive them, and move on.