How many bad addresses do you get from ListSource?

[Sean Cole]

I recently bought a list of about 8500 names from ListSource to use for some marketing (absentee owners).  I'm curious what kind of failure rate others have experienced with them, because I'm sitting on about 500 returned postcards already (more coming every day) out of that list.  All told, I'm in about $1 per postcard between the list purchase and the cost of the mailings, not counting my time to go back and clean up the list I just bought.

That seems like an awfully high "failure" rate to me...  The cards are all labeled "Return to Sender.  Attempted Not Known" or something similar.  It's not a mail forwarding issue where people have moved - it looks like they're just bad addresses.