All of the sites should have a clear statement of what is going to be graded as plagiarism and copying.
I have had a number of assignments I graded that have been both approved and punished for plagiarism. Some had no sources and were copied and some had sources and no quotes around copied material.
Even the HM told an AT that it was not plagiarism if it was directly copied and had quotes, but that is just another form of accidental plagiarism.
The guidelines should be the same across all sites. Either no decrease in a grade for any form of accidental plagiarism, or a troll grade for anything that does not use a proper format like MLA, APA, Chicago style, etc.
Otherwise it is up to interpretation and it really turns one off to want to even grade homework when points and IG currency for grading is lost because of what level of plagiarism is allowed being open to interpretation and even having a "pick and choose" aspect in the HM's opinion of what is acceptable.
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