In many cases, a serial number alone will NOT tell you if a lower is pre-ban or not...

thee12nv,

The normal process is for both parties to agree to a 3-day inspection period from the time the gun arrives at your FFL, during which time you can decline the purchase and receive a full refund, minus shpping. You may want to clarify if weekends are excluded, say, if your FFL is closed then.  You (the buyer) agree to pay shipping both ways if you decide you don't want it, UNLESS the item was clearly not as it was represented, in which case the seller pays shipping.  Once you have accepted the purchase, your FFL completes the transfer and the transaction has been completed.

The above is more or less the industry standard, and you should suspect anyone who isn't willing to abide by it, as it protects everyone pretty well.

-Troy