While a good outline is better to work from, even if you get a shoddy outline, you're ultimately just using it as a base anyway. You're still going to need to put time into updating it and incorporating your notes from reading and class. So if the author of the outline missed some stuff, or worded things differently than you have them from both class and reading, then you can change and correct it.
But otherwise, asking for their grade is really the best way to judge. In my experience, most people are pretty up front with outlines, saying they either did pretty well, or the person *they* got the outline from the year before did pretty well, etc.