Every family is going to have their own list of deal-breakers and my best advice is to figure those out in advance and go in with your eyes open.
For example, for us the proselytizing types are a no-go. Because unlike many in this thread, we aren't atheists, but our religious choices are actively offensive to fundamentalists. We don't want to hang out with people who are going to be offended by our existence.
On the crunchy unschool side, we get along better, but we do require a certain amount of... er, civilized behavior, from these children. That may sound like a surprising comment, but for every unschooler who's directing their own education but is otherwise a creative, lovely child, there's another who has zero sense of boundaries or appropriate behavior.
And while I realize that other homeschoolers are terribly convenient from a scheduling point of view, especially when kids are young, DDs current crop of friends are all public school students (some who homeschooled previously and some who are part time public and part time homeschool).
