the little welders we had were abused like no other. concrete poured on them, dropped from heights (one didn't make it when dropped from the 3rd or 4th floor) thrown around....like stated, change the liner, they are easy to get kinked and that wont make welding pleasant. sometimes though when people have the wrong rollers for the size of wire, like to small, it will take off little shavings of the wire and clog up the liner. so if you do get a used one, i would first take the whip off and use some compressed air to blow out the liner. the connections going from the whip to the machine (the little pins that have a part that screw on), are not the strongest so be careful with them. the one benefit with new though is the warranty. if i were to buy one though i would have no problem buying a used one as long as i could run a weld to test it out and see if any problems occur and what it would take to fix.