If it hasn't yet gotten to be soiled, protect it now.
I've done extensive tests with both water based and solvent based protectors made for upholstery, and what I've learned is that once a fabric is properly protected, it can be cleaned with more safety AND better results than if not protected.
These results are measurable, but not as readily noticed in synthetic fiber carpet. In the case of delicate natural fibers, though, the differences are impressive.
Dyes will be more stable, because you won't need to use nearly as strong of a cleaning agent to get them clean. They also will be more stable because you will be cleaning the soil and the "outer edges" of the yarns. Your cleaning agent will not penetrate more deeply and begin to cause bleeding or fading.
Browning becomes just as unlikely, for the same reasons.
I've cleaned protected natural fiber fabrics with cool water and a microfiber cloth. This will render better results than dry solvent cleaning and is as safe, if not safer.
If they don't accept your offer to "vacuum and protect" this sensitive fabric now, they are foolish. The use of the cleaning method I recommended might be helpful, could be safe, and will have some soil removal, but the results will not be nearly as satisfactory as they would be (nor as safe), if you protect it now.
If you find hemp that hasn't been protected, or if these people have no sense of responsibility for their belongings (I know I sound harsh here, but if you present these benefits and they won't do it in light of what you're offering, they are both foolish and irresponsible), then you can try the cleaning method I recommended.
The use of absorbent powder in the customers home and allowing it to work over night without you there is probably not a good idea, but if you find the need to do it, you can purchase diamtomaceous earth from most garden supply or pool supply places. Its used for filtration and pest control. I've seen it at Home Depot.