Well, You've got the best cowboy car cleaner right in front of ya.

I clean my and my mates car seats with a special goulash.

Eco washing fluid (Eucalyptus scent) and warm water and a cloth and very very soft leather brush.

Half a cap of that fluid in about 5L of warm water. Start gently lathering it in, then dry towel it off.
Use a vac to remove the rest of the free'd up dirt and moisture.
Leave a dehumidifier in the car for a day.

So far its worked perfect on blue suede, my cloth interior, a cream white interior and had no marks or defects.
I tried those crappy things with the plastic bristles on top in a can and they just make a huge mess and spread the stains.

Carpet cleaners often clean car upholstery. Give the person you get to clean your carpets a call and ask for a price.

For fabric seats with stubborn stains of mysterious origin I use paint thinners. Don't forget to ventilate the car afterwards.

PS. For light coloured vynl seats with stubborn dirt in the cracks I recommend toilet soap with a soft brush.