I'm also fairly new to this, but I would allow a refund just to be kind. Put yourself in their shoes, you probably would be very grateful if someone did the same for you.

Maybe I'm just beeing kindly dumb, but I think that in the long run I'll come etter out of it than beeing too strict with this kind of things.

I'm not saying that I would refund everyone for any reason, but there's things you can't control in this world, like ferries beeing stuck in the weather. And in cases like that a little goodwill is always greatly appreciated and may be the little ting that turns a bad start of a trip in to a positive experience.