I'm kind of curious to see what other people think about this thing. Do you think these sorts of posts should be allowed here even though paid advertisement is already kind of a thing on e621? I could have sworn I've seen posts get deleted because they were like, shameless self advertisements for packs and patreon and such and assumed they weren't allowed even though its still happening. It just feels like these kinds of uploads don't really belong on this sort of image board.

"Should cropped advertisements be allowed"?

Out of context, no, either cropping the image to focus on the advertisement or cropping out the advertisement would be less than ideal; if the image doesn't focus on the advertisement then it may be approved after being uploaded, and if there is an image that doesn't contain the advertisement (but is still the same image, resolution and everything) then it would be approved over an image that had the advertisement cropped out.

Long story short: don't bother uploading images that contain(ed) advertisements, edited or otherwise. The post will likely be deleted.

We have seperate section for advertisement in guidelines.
https://e621.net/wiki/show/uploading_guidelines#ads

If post has blatant price tag or patreon logo over genitalia, that's almost immidiately getting deleted. Crops are instantly deleted if they are done by third party. Crops by first party can be accepted, but if full version gets posted that usually renders crop inferior so there's not too much point in them - especially when most cropped artwork also have text where to buy it, rendering it unacceptable advertisement.