Hi, we have been having our hardwood floors refinished. They are old (narrow board) floors that were in very good condition prior to refinishing. We wanted darker floors with a clean finish that would have a long-lasting durable finish prior to moving into our home. The floors have been sanded, wood filled, stained with Duraseal Coffee Brown and one coat of oil based poly (Masterline Commercial grade). After drying our floor refinisher called us to let us know that the floors have dried unevenly and he was concerned. He wanted to lightly sand the floors and change to a water based poly. He left us a small sample in one of the rooms. Should we be concerned that he wants to put a water based poly over top of the oil based he has already put all over the floors in every room? Will we end up with the finish we wanted - a darker, with some depth and clarity, long-lasting durable finish? Should we be concerned?

I don't know what kind of problem your refinisher thinks he has come across.
A dark stain takes longer than a light brown stain for it to dry completely before the first coat of finish is applied because it has pigments along with dyes to darken the wood. Usually one type of finish is applied for successive coats. Water-based finish sticks to regular poly when it has dried properly, though.
Your contractor will be on the hook because he has a warrantee if there are any problems.

Thank you. We will let you know the outcome.