While it’s ultimately up to the person doing the hackintoshing and thus an “honor system” thing, all the guides are pretty explicit about how you should generate serial numbers that are syntactically valid but cannot belong to real machines, for example that of a 12” Macbook manufactured in 2020 in Cork, Ireland (no such machine exists, as they were discontinued in 2019 and manufactured in China). That way there’s a small chance of collision with other hackintoshers, but no threat of accidentally using the serial of someone’s real Mac.
While it’s ultimately up to the person doing the hackintoshing and thus an “honor system” thing, all the guides are pretty explicit about how you should generate serial numbers that are syntactically valid but cannot belong to real machines, for example that of a 12” Macbook manufactured in 2020 in Cork, Ireland (no such machine exists, as they were discontinued in 2019 and manufactured in China). That way there’s a small chance of collision with other hackintoshers, but no threat of accidentally using the serial of someone’s real Mac.