Alright, here's the thing. I have a chance to buy a used Tascam 688 8-track recorder for $660 (that's with shipping included). This looks like a great unit, it even comes in a hard case. I am able to purchase it through iescrow.com, which allows me to evaluate the product before the money is sent to the person. Now, I really want this unit, but I don't know what I should do to make sure it's worth $660. What should I look for/do to make sure everything works right, and is in good shape. I should probably replace the heads when I get it, how much would this cost? What else should I get replaced? And how much does it usually cost for a tech to take a look at it all and fix what needs fixing (rough estimate)?