Garage Floor

I just had a garage built which is attached to my house. The builder/contractor never made any saw cuts to the concrete floor. Now only months later the concrete floor is cracking. I understand that concrete is going to crack anyway but my questions are as follows: (by the way the contractor left us high and dry)
1. How do I know if the cracks in the floor are not normal stress cracks
2. Should I now make the saw cuts
3. I would like to seal the concrete floor. what is a good sealer to use.
Any other advise would be appreciated.
Thanks in advance
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