It depends on the company. Some will compensate with free products, others will pay a salary depending on your job role.
I can't speak for other companies but we pick reps who have a passion for our products. We have no interest in hiring reps who apply to join several different companies. They have to genuinely rate PES products otherwise we are hiring an actor to pretend lol.
I hate seeing people join companies and instantly start promoting products which they had never mentioned before. It is very transparent at best and at worst it is deceitful to the consumer.
My two cents.