Thought I would add my bit to this thread. 
  
I too work full time and have plenty of time off and am a part time pest controller. Works well for me as sole trader, but to really make it you WILL need a partner who you trust to share the work and money, so if your working and cant do that urgent rat job, then chances are your mate could. Saying that, i dont use anyone else, and for most people thay will wait for me, if they cant then too bad. 
Join the NPTA National Pest Technicians Association, go to their Pest Tech 14 day (details on their webpage - NPTA) they offer loads of courses to help