Stains can accumulate over time and wear out from things that you may have dropped on the seats.
I love Oxi Clean and it works well when I use their products to clean.
It cost only about $3 to buy this products and it works well to remove the dirty stains.

Image by iDV Create via YouTube
Materials:
Directions:
First, spray the entire seat with the cleaner generously.
Let the product cleaner sit for about 30-50 seconds and use the brush to scrub the stained area.
Its important to not wait too long or the product will soak into the seats.

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Next, keep applying the cleaner and using a brush to scrub.
Repeat the process of respraying the product and scrubbing if necessary.
Overall, this would be a great way to tidy up the car seats from the dirty stains.

If you dont have the vacuum use a microfiber cloth and a bucket of water.