Ah yeah, that is a bit frustrating. I suppose I can give a hint for Mary (because that's the only story I've finished so far), she likes video games, which you quickly learn. The arcade sells items.
You can also infer that she likes games from knowing she's a pastry chef (and knowing that the B&B place is a pastry place) and seeing her playing a game there. Or just randomly encountering her there in the evenings playing her game console.