We recently bought a house (it was a flip) and it had new flooring installed. It’s laminate flooring. As I’ve walked around the house I’ve found spongy areas that give really easily. We have a crawl space and I went down there and the foundation looks fine as do the joists . The inspector cleared everything down there as well. Curious as to what is causing these areas to give whenever weight is put on them . A friend suggested the sub flooring wasn’t attached correctly or at all but I’m a novice and wouldn’t know where to look .

Any ideas as to why this is incurring ? Whom to I call to fix this if there’s an issue? A flooring company?

I’m also curious if there is an issue and others have had this issue after recently buying a house, if fault falls on seller of house or inspector for not finding it? I just would like my floors fixed honestly .

Laminate floors only set on the sub-floor if the floor is not flat then there will be low and high areas where the floor will move more than the manufacturer has allowed. If the floor was not flat when the flooring was laid over it you may not have a warrantee that covers defects in materials.
To fix the problem, you would need to take the flooring up and flatten the floor underneath. This is a big job and some laminate may not be able to be used again.
Some pad foam used under the laminate will help with flattening as the high areas will compress the foam over time. If a contractor laid the floor he should have read the installation instructions and followed them to give a long lasting product.