I've bought some items from all these shops. What I've felt is that prices vary slightly between Dubai autos, Racing Dubai, and Shahid autos. Of all three Racing Dubai has the largest collection of detailing products. He has some items that Shehryar doesn't even know about. But for some items Racing Dubai is expensive.
Bottom line:- Never rely totally on one shop. Do your shopping product by product. It's quite a 'khawari' but this way you can save some of your hard earned bucks