This is known as hydrostatic pressure and if considerable will cause sealer to cloud and/or peel eventually.
A test is to take 6 mil visqueen [heavy transparent plastic] and tape to the floor.
24 hours later take a look under the plastic. If there is considerable moisture, beading water,etc. you have hydorstatic pressure and will have to go with companies like Penetron [NY] or Xypex, even Tamms Industries.
Next, preperation for both floors is necessary for sealer to take. Sweep large debris, shop-vac smaller, power wash or soap and water if possible.
Allow to dry thoroughly.
Sealers primarily come either water or solvent based.
Water based are odorless and easier to purchase. They require being applied more often. They do not build to a sheen.
Solvent based have extreme fumes, are flammable but remain tenacious for a longer time than water based.
For either go with 30 % solids minimum. If you opt for the solvent, you will need a respirator. I would not ecommend this for indoor use at all. It will permeate floors, walls, rendering open food indigestable, etc.
Personally for homeowners and DIY's I recommend a water based concrete sealer.
Brian T. Chaffee
Custom Stamp Concrete