Well I must say, just to give foster caters their due our fcs were amazing and I felt fine in their house. BUT it was still nerve wracking and tense, and tiring!
I'd also say just smile and wave. As others say. Really like the penguines on Madagascar! Because once this week is over, your child is your child and the fc will not be in the picture.
Use the time to find out all you can. Also ask to see photos and ask for copies, DVD footage, always saying to fcs how great it will be for child to see footage and photos of themselves and of fcs.
What do you mean when you say little one spoiled? I'm curious because it means different things to different people. It may also depend on age of child. I mean we might do more things for a three year old child who is in foster care than a three year old who is not, because we want to respond to needs in a certain way (Eg helping them do things) once truly settled into new family it may be less helping and more encouraging them to do some things for themselves. If you see what I mean. Plus once child is yours you won't need to 'spoil' them bit you may need to transition that slowly.
Lastly, you may want to 're-think how you describe the behaviour, it may 'appear' bratty but that suggests the new child is a brat. They almost certainly will be actually acting out from a varierty of confusing emotions and you will need to understand why they behave as they do, IMHO.
So you could use this time to gather all the info you can on your new child and how foster caters have handled things.
You won't need to do things the same way but it will, IMHO, help you to know how foster caters have 'coped' with behaviour in the past.
All the very best . 