How should I safely buy/sell a preorder for Bitcoin mining equipment? Suppose I need to buy/sell a preorder for Bitcoin mining equipment.  What is the safest approach (for both the buyer and seller) to conduct this transaction?

Does it matter if this transaction is done over BTC vs Dollars?

I'm assuming an escrow is needed, but not sure where to find such an arbitrator.  If multisig transactions are used, I'd like to see how this would be set up.
They do it all the time over at the 'Group Buys' section of the bitcointalk forum. Have a look at how they have theirs arranged.

https://bitcointalk.org/index.php?board=137.0