What's the best method to clean a wood floor before refinishing?

[highup]

Here's an entry of solid oak, possibly a glued down Bruce floor or something similar.
The customer has a front and a back entry to the house. Both have the same flooring.
I suggested to the customer rather than replace this wood to sand it and refinish it.
On the first step into the entryway there is a dark area. Maybe it's the rubber from a certain type of shoe and maybe it's some asphalt or grease, I don't know. It's been there for a long long time.
Other than discoloration in the floors and fantastic shape.
Is it possible to clean the floor first then sand it lightly and put on a new finish coat?
The edges of the herringbone have a bevel and if it was sanded heavily as when using a drum sander, it might be difficult to keep the bevel even.
I recommended to the customer to try and save this floor rather than replace it since it matches the back entryway.
For a start, what type of product could be used to clean this floor before resanding it?
I'm just figuring if it can be cleaned well it wouldn't need as much sanding.
I told the lady something like Murphy's oil soap would probably be a bad idea. That said, I don't have any good ideas, so that's why I'm asking.

 

[highup]

Okay let me try a second time, here's the picture of the wood entry that I think needs cleaning, before sanding. Some idiot didn't insert the picture.

 

[C.J.]

That’s a neat lookin floor. Makes me think it was made out of 2x4’s or maybe I just wanna make one out of 2x4’s.

 

[highup]

The home was built in 1912 and it was relocated at some point in time. The front of the house is on the back side now, and this was at one point in time actually the back of the house. It's kind of like the house has two front entryways. One in the front and one in the back.
.......which is the front.
I measured the home for carpeting and was supposed to measure up this entryway for cortec or another wood flooring product.
Once I saw the back entry matched the front entry.
.......which is now the back entry
Okay, I'll stop the confusion.
I just think that the two entryways ought to match, so I suggested sanding and refinishing the floor which might cost about the same amount anyway.
Like sanding a car before repainting it I know they also clean it first before sanding.
Since this floor hopefully can be lightly sanded.... .. I'm trying to think of a floor cleaner that might not conflict with the final finish.
Mineral spirits comes to mind but some of this darkness might be organic, like old worn in dirt. I don't know....

 

[DarisMulkin]

Okay let me try a second time, here's the picture of the wood entry that I think needs cleaning, before sanding. Some idiot didn't insert the picture.

Looking at the pictures makes me wonder if the don't have a blacktop drive. Looks like the oil from the asphalt is tracking in. Try mineral spirits to see if some of it comes off. Mineral spirits is a safe cleaner on wood I believe.

 

[highup]

I didn't pay attention to their driveway, but it does look like that.
I don't know what kind of work the lady's husband does. Could be he works in a shop of some sort. It's a nice and well kept home and this floor has been down for a long, long time.
I was thinking of advising that they clean it first because if it's not going to be sanded heavily one would want to get the soil out of the deeper parts of the grain first Maybe some thinner and a fine but stiff brush, maybe even a wire brush.

 

[DarisMulkin]

Use non-flammable though or turn out the pilot lights, I'd hate to see you burn down a house.

 

[highup]

I'm not doing nothin'
All I did is measure up the house for carpet. I was just going to offer some advice to them to clean that dark spot a little bit prior to doing some sanding