I hope this helps but my answer is that I wouldn't pay anybody to take pics of my car.  
I like to look at my car (before I get in!) and try to keep it clean because it looks so much better when that's done, but I found it a bit odd when people had screensavers of their own cars and I certainly wouldn't put a photo of my car in frame. 
That might just be me though and if there is a market I wish you every success.   
If you can make a living, doing what you love, then go for it!!