I'm going to say mould - no. If they cannot hire a cleaner on a one-off then don't go. Babies will put mould into their mouths. I'm no neat freak, I let DS eat food that has dropped onto my floor, I think that a BIT of dirt is beneficial, but mould is NOT. It is a completely different kettle of fish. Mould isn't like dirt - it is alive. And can cause allergies and various VERY nasty tummy bugs. Animal hair can also cause allergies and hairballs - yick.

You shouldn't have to grin and bear that much mess.

Empty cans, baby can drink the dregs and/or get cut.
Crisp packets are coated in salt, not good for baby.

Oh, I would not allow it. And I am a strong believer in family (I haven't cut off my mother because DS should be allowed to see his grandparents) and not a neat freak. There's messy and there's dangerous and no way should a baby be in a dangerous situation. It's not just the hygiene, it's if there's that much mess and baby pulls up, mess collapses, baby falls, baby is covered... can you find baby in time? A knock to the head on a clean floor can be bad, but if baby gets a cut on a really filthy floor covered in mould and animal hair (and possibly traces of animal droppings...) - also, with that level of nasties, there may be rodents. I just wouldn't allow it. You have VERY good reason for not letting baby stay there.

Hope this didn't offend, but words like mould really ring alarm bells with me.