I wonder about chances of success. Like you, I'll be interested if any response by persons more qualified than I am. But having lived here 16 years, I question whether there are enough people who will want to clean their interiors to make it pay. Just look at the condition of most cars on the streets. Sure there are certain to be some, but my feeling is that the percentage of car owners who would make use of such a service is far below what it would be in the US, for example. Also, people with the really expensive cars often have someone who washes, waxes, and cleans the interior of their car at times when they are not using it.
Good luck, if you proceed.