We only opened up our relationship about 6 years ago, but we definitely learned a lot in the first year or so about what we wanted and didn't want. It can be challenging to find quality people (meaning those who are taking the self-responsibility and communication parts of poly seriously). But over all, we have been fortunate to have never had a truly bad experience. We've definitely had some that were better than others, but I also think that some of this comes from the fact that James and I only play together. We've got a good core foundation and then we look for someone who is a good fit for that. At times we've relied on the judgement of someone else that we know and trust to add in someone else, and that has worked well too because we're kind of all on the same page. For example, for James' birthday one year we had our lover Tamara over and she invited one of her friends who we didn't know, but we trusted her judgement so it worked out great.
We don't date around much any more, preferring to stick with the few people we know that we can trust and get along with, except for the rare exception such as James' birthday that time. Discernment does come with experience.