He can ask revisions infinite. It is your duty to include in your offer or description what revisions actually include.
In that case once buyers wants more he already knows he will have to pay extra.
Let me dig up one of my offers so you get the idea.
As per our conversation, I am sending you an offer that includes:
a) facecam frame consisting of one rectangle with oval corners and two colors; gold color with shading/gradient outer edge, and inner red. Additional drop shadow will be included in a separate layer for modification/removal
b) files will be delivered as PNG at price 10$ (creation) and source file PSD 5$ file format.
c) files will be delivered in 3 different sizes, all in the ratio of 16:9, the largest being 1920×1080 and following 65% and 40% of that size.
Revisions included in this offer are only for minor touchups on the colors used. in case color change is asked it must be shared with the exact HEX code of the new color.
Any additional revision is charged extra.
Marina Art Design
So detailed detailed detailed as much as humanly possible.