Pentax 50-135 - why is it always

I bought it from Amazon Warehouse as a used lens so I can return it within 30 days to Amazon but no warranty from Pentax.  Like I said, I think its working ok so I'm going to keep it and take the risk.  If it needs to be repaired at some point so be it...I only paid a little over $800 which is much cheaper than a new one.