2nd hand sounds like a bargain - but you could be buying a whole heap of trouble (as you are new to this sport - errr - hobby).
Your safest and best bet is to go for something new. The ION is probably the best starter marker at the moment (hell of a load of bits and plenty of people to help) - so I'd go down that route. If it does screw up for any reason - there's always the warranty (12 months on new stuff!).
Once you know which end the bullets come out of - go for something a little more 'up-market'.