Thanks everyone for the great replies, which seem to reflect both sides of the meter - OK to ask and not OK to ask, although most seem to favor asking. In my particular case, I did offer to pay for the return shipment, but did not consider a sellers concern for potential damage to a unit, as onhwy61 points out.
So far, my take-away from responses is its OK to ask, but most sellers will likely say no, so if you move forward make sure you use a protected payment in case of dispute, and know the resale value of the component if all goes awry.