Yet another buyer protection fee thread

I'm sure I'm not alone in having not quite got my head around this yet. I have an item for sale at the moment... It's up for £275, which with the buyer protection fee comes to £286.72. Someone has made me an offer on it: my seller dashboard tells me the offer is £270 including buyer protection fee; in other words, the offer is £258.92. Does that mean that the buyer has offered that very precise amount, or that I'm paying the buyer protection fee on a £270 offer? I can't quite wrap my head around those figures. All advice gratefully received.