I would recommend pre spraying the rubber floor with Bio-kleen at 5-1 and let dwell on surface for 2 minutes, Bio-kleen is non-caustic,non-corrosive, and totally safe to use on rubber flooring.
Then use a damp microcleaning mop pad to deep clean and pull to the surface all the ingrained soils, finally flat mop the floor with a damp waffle microfiber floor cloth to absorb all the loosened soils. guaranteed your customer will be delighted with the results.

Regards
Tadgh