My cottage is right beside the shore on a tidal estuary. When I welcome guests and show them round, we talk about the ever-changing tide and I show them where it rises to. Everyone understands that the tide goes in and out and I've never found it an issue.
If you don't meet your guests on arrival, you could put together a simple information sheet, maybe with photos of high tide and low tide, print it out in colour and frame it, then have it on the wall somewhere prominent, or have it in your welcome folder/house guide.
You could also say in your listing description something about watching the tide rise and fall, or go in and out if people really don't understand rise and fall. You just have to inform them.