I think it really depends on the type of script that is being reviewed. If someone buys a scoreboard, sees every picture of it, then drops a 2/5 star review because its "ugly", that's not fair. The buyer knew EXACTLY what they were getting into, so they should not be able to leave a bad review in that case.
I feel the hard part about reviews is just how misleading they can be. You can have a script that you entirely rewrote, but because of your old and bad reviews, your new versions don't look good. I propose something to do be done almost like what Apple does with the App Store. They display the review statistics for the current version of the script, with the ability to look back at the previous reviews. Because gmodstore is on a much smaller level than the App Store, it should also be done by classifying something as a minor or major update. Minor should keep most of the previous reviews, major should be almost like a new page.
Another thing I really don't like is that kids can leave a bad review because they don't like the way you coded it. By that, I mean your coding style, ex. indentation length, spacing, etc. It's one thing if someone's code is just horribly unoptimized and lags your server, but it's another if the way they write it is not up to your personal preference.