Refinishing wood floors is a tough job. When hiring someone, here's how to know if they are top notch. (If you're doing the work yourself, try to hold yourself up to these standards).

Visit other homes they have worked on. Get down on your hands and knees and look out for:

Swirl marks in the wood -- They should know how to use the right type of sander and sand paper to avoid sanding marks. This will be difficult to see on floors with a satin finish, but look closely. Ideally there should be none!

Inconsistent color, stain, coverage -- particularly in doorways, around appliances and baseboards

Problems in transition areas --  In a kitchen, look under the appliances. Is the coat even or did they quickly brush some varnish underneath. Open the refrigerator and look down at the floor -- see any problems?