Baby walker (those that baby sits inside with wheels at the bottom) was banned in Canada in 2004, so if you bought it before 2004, the previous seller was ok, but if you are selling it now in 2007, you can be sued and the penalty is severe. You will be held liable in a civil court of law for just selling it second hand.
Same rules apply to used cribs, used toys, used playpens, used strollers which do not meet the current Canadian standard according to Hazardous Products Act.