What does the sales trainer do and how he should be?

For automotive , sales trainer should know all weakness a strengths of the cart that they want to sell and inform the sales team , and for Persuasion of customers they should know some Technical information to answer their clients questions , Note : They shouldn't focus on the Technical information and make their customers boring ,

It all depends on what one plans to achieve thru the sales training program thru the sales trainer.
It' a chain effect.
Plan and set the objectives / out come results to be achieved out of the program and co-relate the effect of those outcomes on the business plans.
Make an assessment of the manpower sales training requirements.
Based on those objectives, one can decide what all one requires in the trainer.
Such as: Technical Knowledge? Sales knowledge, sales, training and on the field coaching experience? Trainer's skill sets? However, apart from the other requirements, the trainer must be an effective communicator and listener.