yes, but the KNOWING the client is guilty bit can be taken with a pinch of salt. I used to work as a legal exec for a criminal firm pre-children and I'd say that 99% of our clients were guilty as hell but we still had to defend them, we just didnt ask if they did it (not that criminals tend to tell the best truth to begin with!).
We had some horrible clients, but money is money, my boss used to even keep hold of them as clients if they had been violent to us in the police stations or at court as it was money. Hence, I no longer work in that field.
We also had some great characters who you certainly wouldnt want to meet in a dark lane but used to come into the office and make us laugh, the more stupid the more amusing really. Oh and criminals universally smell but we still had to stick by the smelly poo-smeared addicts (unfortunately)
I guess if you are the boss of a firm you can refuse to act for someone you dont like, but if you are a skivvy (not a partner) you have no say. I got assaulted by one of our clients in a cell at Crown Court when I was 4 months pregnant with dd, and to this day my boss still acts for the git. Something to do with the 20 odd arrests per year and it paying his sallary. Hmmn.