There are some good travel companies in Kerala. A list is given below.
1.Kerala Taxis, 4 stars, 4.2 rating, Cochin.
2.South India by car & driver, 5 stars, 5 rating, Kerala,
3.Wheel Man Taxi Tours and Travels, 4 stars, 4 rating, Trivandrum Cochin, Kerala
4.Car hire, Kerala 4 stars, 4 rating, Cochin,
5. Kerala Tourism and taxis, 4.5 stars, 4.4 rating, Kerala.
Last year when I toured in Kerala My brother who was staying in Cochin used to organise vehicles from the above list. I have not faced any problem. The vehicles were in condition and the drivers are very accommodative and guiding us.
If you want any further details you can search the site: Kerala taxi.com