Yes this has happened to me also.
The guest booked my Studio for 2 and 1 child 4 yrs. They enjoyed their stay and loved the accomodation, very complimentary.
It is stated in the fine print that the studio is only for couples & a fold out is available for 5 and under or portable cot for a baby. Additional charges apply
The fold out bed was provided for a 2 night stay as per the booking
The guest contacted me on departure to advise I had overcharged them. They advised that the fold out bed had not been used as they all sleep together at home and they all slept together in my Studio. The guest demanded a refund and was insistent that the bed had not been slept in.
I stood my ground kindly & nicely stating Health & Safety Regulations about sleeping arrangements in my property. Every guest booked is supplied a bed & linen
I stated that I need to provide bedding for all guests including children under insurance requirements.
The guest gave me a nasty revenge review, even though I provided everything required.