What are the essential trainings any salesperson should follow?

sales skills the first thing believe on your talent and then .

1- Sales Fundamentals
2- Persuasiveness
3- Maintaining Self Confidence
4- Building Strong Relationships

- A salesman must have these basics as a start :
1- Must be positive even when he faces setbacks ( when you are positive you can always find solutions).

2- Must have the right attitude, very precise setting his goals " targets" and very flexible on how to achieve it " trying different strategies as needed".
then he must have a descent level of self confidence, to be aware of his product well and the type of customers he is targeting.

Any successful salesman must be at good level of attitude and behavior because most likely you will meet various type of people.
So attending courses or trainings which focus on improving individuals behavior and attitude will help to approach customers.
Secondly ,Eduction is the key here, if you want to talk like a pro during meetings and face-time you must have an idea about ever single segment.
You should be able to talk about: Finance,Marketing,Management,Accounting, etc.....

The most essentail 

communication skills