I actually think anything below 10% is safe, but the bottom line here is, if the advertiser complains to the network. the networks complain to you and I think conversion rates is not a big thing to worry about.
Think about all the conversion rates they send around ie, xxx offer converts at 30.92%. so are those guys gonna have a problem? They have this all over just talk to your am and i'm sure he/she will hook you up.
I am actually in the same boat at the moment, I choose not too worry about it, since they haven't complained at all. I watch my email like a hawk and so far so good.
I just keep in mind, if you're doing something wrong and they caught you USUALLY they notify you immediately, at least in my experience (just like my post above)
All the best,
Catz