T.B.
I'm posted as a childcare provider on Care.com and have had my last 3 jobs from there.I'm also posted with sittercity and haven't gotten no feedback.
I've found no problem with the Care & would recommend that you, as a potential customers try it. I've never received spam or had a scam and the only way others get your info is if/when you give it to them.
There are several postings of parents looking for in home nannies. The sight really varies on the job titles!
If worried about the person - ask for references that you can check and see if they have a backgound check on the site. Also, see if they have any feedback on them.
Good Luck!