The following is the only way, as a buyer (and a seller), I would do business on Audiogon (especially if the product is over a $1,000):
1) Check the sellers feedback, if there is negative feedback or none at all proceed with extreme caution.
2) E-mail seller with the following questions: explanation of rating, why it does not come with obm (if no obm), why they are selling the unit, are they the original owner, and age of unit.
And, most importantly ask if they will do cod with a deposit (either you can send them a money order or you can paypal them). The amount of the deposit would be the amount of the shipping, insurance and cod charges and a little extra for their time. If these terms are not acceptable forget it. LET ME REPEAT, IF THESE TERMS ARE NOT ACCEPTABLE FORGET IT. Don't get emotional and make an impulsive decision and lose your money.
3) If all checks out, ask for a phone number to call the seller at. Call and talk about audio, if they have been in the hobby a long time and are knowledgeable, chances are better that they are responsible because they probably would want to use Audiogon again in the future. If they appear to be credible send them the deposit. You've done all you could to ascertain that they are not flaky.
Of course, all of the above is discretionary, where their feedback is abundant and positive and the product is under a couple of hundred bucks you just may prefer to send them the money in advance.