Insight & Examples - How do you charge/bill for any commissions for payment as a freelancer?

[msml2020]

Hi, I've been seeing more and more commission based work which I don't know how one could even charge for that based on Upworks standardized hourly or mile or project work standard template. 

Just curious how that would work and if you have done commissions only work before can you show an example of how you had set it up? 

Can you share your work experience with the commissions only role? 

Thanks in advance.