At the time of purchasing a house, it is a good idea to hire a house inspector to inspect the house thoroughly because then you can still negotiate with the seller if something isn't quite up to the mark. At least you can request the seller to have the problem fixed before handing over the house keys or the seller might offer to reduce a bit on the house price due to the problem. Something like a creaky and squeaking hardwood floor doesn't show during the summer months but come winter time, the hardwood floor can start squeaking and creaking a lot.
One of the tip you might want to try is to increase the temperature of your house heating during winter months because at times, when the house internal temperature is cold, the hardwood floor makes creaky noise. There are also other kits available in the home hardware stores to fix the hard wood floor creaky problem. It consist of either screws type of kit or the aluminium brace type. Below are pictures of both the type of kits: