I always start off by going over the whole floor on my hands and knees. This is only way to check an old floor for split boards and broken top grooves. I may find at this point that the floor is just too thin or damaged to handle the extensive sanding process that a stained floor needs. This is the time to decline a job. Before you end up with bad results, and every body blames each other. Just remember in all the small claims court cases that I have served as an expert witness, it was assumed that the floor mechanic alone had the expertise to determine if a floor could be sanded with good results.
Now if you are a amateur and have never done a stained floor before, and you think you are going to simply rent a floor sanding machine and sand the floor yourself, please consider this. I have another (free) article that discusses in detail whether you should consider doing this rather difficult job yourself. You might instead, hire the pro to do the floor sanding only. Have a professional follow the prep for staining as I will describe in this article. If he won't do all the details I mention, do the final vibrator and buffer sanding yourself (and this you CAN do, and they do rent good equipment for this).
This way you can be sure that all the proper steps were taken to prepare your floor for the wood stain. This article will be cheap insurance really. You will know exactly what to look for after a floor is sanded, (before you pay) so as to avoid even this contractor leaving machine marks. Might have him read this article, so that he knows, you know. A proper "sand only" job will cost about a buck a square foot or less.
A well sanded floor will be a breeze to stain and finish, and this article will save you from hiring the wrong contractor. I do have another article on how to stain a floor, and another on how to apply polyurethane to a floor. These tasks are often done better by the knowledgeable amateur as opposed to the so-called pro who is in a hurry to make money.
Step 1: How To Sand Wood Floors: Without Leaving Machine Marks Introduction
Step 2: How To Sand Wood Floors: Can it be Sanded?
Step 3: How To Sand Wood Floors: Start with Fine Tuning Your Drum Sander and Choosing the Best Sand Paper
Step 4: How To Sand Wood Floors: The Right Sand Paper Makes The Job For The Initial Rough Sanding 36 Grit
Step 5: How To Sand Wood Floors: Repairing Gaps and Second Sanding Stage With 60 Grit
Step 6: How To Sand Wood Floors: Final Drum Passes with Burnished 80 Grit or Regular 100 or 120 Grit
Step 7: How To Sand Wood Flooring: Edging - Using The Edger Without Effort
Step 8: How To Sand Wood Flooring: Screening and Final Preparation For Staining or Finishing