After hiring a Nanny through Annie's nannies I found that she had been let go from or quit multiple jobs that I wasn't told about (including at least one placement that Annie's knew about) and that she did not have current CPR training.
When the nanny quit our job with no notice (and owing us money), we tried to use their free replacement guarantee. We had a very difficult time getting replacements from Annie's. It took almost a week to get a response to email and we received three resumes in a month! When we checked into those resumes ourselves (not wanting to trust the background screening this time) we found problems with them as well.