I have a friend who has a 5 year old dd. Whenever her and her dh want to go out together (which is not that often - maybe 6 to 12 times a year), they don't get a babysitter in, but ring round friends and neighbours instead asking if their dd could stay with them - possibly even overnight! She teaches in a lovely girls only school, and her daughter used to go to a nice nursery, so I don't think she would have trouble recruiting a babysitter. But I think she doesn't want to spend the money (she's very tight with money - she once asked me if I wanted to use up a left over, but already opened, pack of nappies - and then asked me for the money for it!), even though they're doing ok financially. And I think the other thing is that she doesn't want to have a "stranger" in her house while she isn't there.
She hasn't asked me that often, because normally she can rely on a few other friends, but when she has asked me I've made excuses so far. But now she's left a message asking me again - and I really, really don't want to - especially as this child is notoriously difficult at going to bed, she's been known to haunt the house until 11 pm! So shall I just say that I'm not feeling good enough (I've got mastitis), or what?