Hmmm that's a really tough one. Although I'm not sure I would like that kind of attitude from my clients. To just say "no". Sounds kind of unfair. You clearly would not do this if you didn't think you could so does this mean they do not trust your judgement? We could all use the extra money, it's not like this is a super lucrative business. But if you can't fill that space... then you lose money there too right?