Actually, there is no shame in using an unknown script or a public translation.
Sure there is ... which is why things are re-translated even though there are public scripts available.
Someone reputable would likely put another translator on it to check it though.
Groups that use this service will probably not have a translator available in the first place. Anyone who does have a TLer will just use him or her anyway. It's a lose-lose situation.
Seriously, if you compare Anime-Keeps translation of Mahoujin GuruGuru with the public translation posted to Scriptclub.org by monmon, theyre pretty much over 90% exact.
But it's the 10% that makes a difference. Out of 350 or so lines, I don't want 35 lines to be incorrect.
Nah ... it's still a bad idea.