I usually avoid Marriage Contract stories on the basis of finding cross-generational pairing generally squicky but I found a rare one... that I liked. I ran into this interesting example in my trevails through the Pit of Voles. Yes, the contract turned out to be fake but...

http://www.fanfiction.net/s/7306781/1/The_Contract

Perhaps it's my shipping inclinations or my funnybone, but in light of the despairing turns the Authors current project is taking (thus alientating many of the current reviewers) I found it quite nice. And that's despite the possible OOCness (being a fanoneer now, My scale is rather imprecise) and general ridiculousness of the scenario.

This is one of TVtropes's "Fandom-Specific Plots" (http://tvtropes.org/pmwiki/pmwiki.php/Main/FandomSpecificPlot, under "Harry Potter"). According to that page, it "originated as a fanfic-writing challenge on a Snape/Hermione mailing list." And I guess for whatever reason, the concept just became really popular with the fandom at large.

There is a question on some Mary Sue Litmus tests that asks: is she trying to escape an arranged marriage?

I'm not into HP and haven't clicked the link, but by "Marriage Law" I imagine you mean: the law says that so and so have to get married. And not some law that says: two people voluntarily sign a contract that they will take care of each other and the law offers them certain tax benefits.

So the idea of forced marriage is a trope across fandoms. It's just that there's more room to imagine there will be laws that force marriage among wizards because they have a different culture.

Arranged marriages may seem romantic to those that never have to deal with them.