I hired a wood installer to handle 1500 sq ft of Johnson engineered BR cherry. I've notice quite a few cracks between the wood. What can be done about this. Several glued down thresholds have come unglued as well. Should the cracks be there and how should you put down thresholds? I hope I didn't get took to the cleaners

The general rule of thumb is that a wood floor can have a few very minor flaws, as long as they can be filled or puttied. Now by cracks, do you mean gaps between the boards? If so, it may be that the milling was poor and the installer had to "cheat" the spacing. Or it may have been a sloppy install. The floor would need to be inspected by a professional, independent third party to determine the reason for the gaps. The floor could have shrunk as well. As far as the thresholds, those can be re glued. The installer should do that at no charge.