We have used babysitting services in a variety of cities. Our rule has always been this: if either parent is uncomfortable with the sitter when he/she arrives (appearance, attitude, whatever), then, we simply tell the sitter, we've had a change in plans and pay them and send them on their way. We've never had to "enforce" this rule - we've always checked out a service, we've also made sure we were acquainted with the hotel concierge and asked that someone "check" with the room - and have told the sitter that the concierge or someone will call or come by to see if they need anything. We let the sitter know where we're going to be. Especially if the hotel has recommended a service provider or two, I feel more comfortable as the hotel (notwithstanding all the statements of "no liability") doesn't want guests to be unhappy or to feel the referral was to an indequate service.