If they see you write down their no. they will kick off or retaliate later some how , had one put a curse on me when he tried to extort £200 and I stood my groundI am always polite, and say a firm "no", and that all our scrap / batteries etc are taken to local recycling place for waste transfer ticket and we are happy with the arrangement. In reality, I want them gone as more often they are not after anything - just having a snoop about. Memorise plate, and add it to the list.