Costs is a big one for families, as well as asking for references. Recommendations from other mothers (friends and/or from your mothers group if you go to one) is also ideal. Otherwise, if you have the funds, and you can recruit well, then why not hire a nanny or babysitter. That way a bond will endure.
As a person who has worked in nearly all childcare roles I think parents should find out if the centre is accredited, what quality accreditation did they receive, what are their staff to child ratios, do the staff have first aid certificates and all the costs involved? A new rule came in recently that all childcare staff must be qualified now which is great news!