I just bought a haome that had hardwood floors installed in 2003 during a reno. Where the prior Owner's had rugs and heavy furniture, the floor is now lighter in color than the the rest of the floor. These floors have an aluminum oxide factory finish. We have tested small areas with several cleaning type products to no avail. I beleive the prior Owner's smoked. I can email a picture if that helps.
Thanks.

The areas have darkened with age and sunlight. There is no cleaner to repair this.
The areas that have been covered are going to be closer to original color than exposed areas you can leave the rugs off and see if it will eventually even out, which may take months or years if at all. The best option is to sand and refinish the floor.