If I have an accepted paper in a conference, and for some reason I will not be able to attend. I may ask another person to present my work in the conference based on payment, favor, or being an author on this paper.
I am giving you an example. I deliver lectures on plant nomenclature using power point presentation. Suppose I become sick and ask someone to deliver the lecture on payment basis. What do you think, it would be as good as my own presentation?
The issue at hand is the content of the paper, not the presentation, so somebody else can present( we write articles, books etc that are published by others!!) I do wish you are talking of meeting the presenters expenses but not payment.
I think that paper presentation should be based on authorship not on and not on favour or in return for payment.
I present papers at conferences so that I can receive feedbacks which I can incorporate so as to make my paper more acceptable for publication.
When I co-authour papers, I make sure that I contribute conspicuously. My co-authours should be able to contribute thus so that in event of my absence, s/he can deliver the paper and obtain the full benefits of the conference!
It is based on authorship otherwise teleconferencing where possible.