If you're going to talk to the person, ask them about anything that is important. Bathroom items? What do you mean? Toilet paper, or soap, etc? If it's French side, don't expect anything. Dutch side, they should provide toilet paper, but soap is a crap shoot. Regarding chairs and umbrella, ask them, but if they don't, you can always rent from Craig at Packlight.

Regarding 'one heck of a deal', just make sure it's not 'too good to be true'. Check the refund policy. Also, hopefully there will be some reviews of the owner, wherever you're booking. Best wishes!