Never buy a Cimex sight un-seen.
If they are handled by chimps and dropped on their base face down a lot, they will run "Sloppy" or "Wonky" and you will kill your back fighting the machine to stay straight.
A healthy cimex should be able to run perfectly STILL without the operator touching it.
My friend who went by the name "amazingcleansc" here bought one, and it had been abused by chimps. Subsequently he had to fight the machine a little to keep it straight. But he still loved it.
So to test one, bring a scrap 4x4 piece of carpet, wet it a little, put the cimex down and turn it on. It shouldn't move hardly at all, if it moves from one side or the other vigorously it has an alignment issue, and you will need to base your $ offer on that.