Purchasing second hand car - should I look for a certification to protect my consumer rights?

I bought a used car from a SIMI dealer using a standard contract.

I had issues with suspension within guarantee period that the salesman gave me the runaround on for weeks.

I wrote to the MD of the dealership a letter and made the threat of taking them to the SIMI disputes panel. In my case it got a response and the problem fixed.
 
In your experience then, SIMI an effective consumer advocate or a chocolate teapot?
 

Thanks for posting. Interesting to hear that someone got action from it.