K.A.
Hello,
Like you I was leery of sittercity.com, but was more desperate since I don't have any family nearby. About 18mos ago, I joined and have used 3 different sitters and been very pleased. All 3 were college students (in their early 20s).
There are definitely plenty of flaky-seeming candidates as well, so you'll have to look through lots of options before deciding who to contact.
Coincidentally, I stumbled across my hair stylists sister on sittercity.com, who we've now used and really like. You may just find that once you join, you'll find someone you know!
Good luck,
K.
Mom to Aaron, almost 3!