Weird gun shop/FFL question

[Patton]

So a friend of mine goes to buy a handgun for her dad and background comes back and she goes to pay for the gun and background, $450 ish, and her only credit card is declined. She knows why it got declined but she doesn't know what to do. She even tries to call me for a quick loan. The gun shop says we will hold it for you. This happened on 12/23, she made it back to pick it that night with cash.
Here is the question. After the 4473 was filed out, was she legally supposed to leave the store and come back and pay for it later?I guess the same day doesn't matter, but what if she couldn't come up with the money or she didn't go back for several days? Would they have to do another background check? Edited December 26, 2012 by Patton

[c.a.willard]

You have 30 days to pick up the firearm after completion of the background check. 

27CFR § 478.102(c):
TITLE 27--ALCOHOL, TOBACCO PRODUCTS, AND FIREARMS
CHAPTER II--BUREAU OF ALCOHOL, TOBACCO, FIREARMS, AND EXPLOSIVES,
DEPARTMENT OF JUSTICE
PART 478_COMMERCE IN FIREARMS AND AMMUNITION--Table of Contents
Subpart F_Conduct of Business
Sec. 478.102 Sales or deliveries of firearms on and after November
30, 1998.
(c) Time limitation on NICS checks. A NICS check conducted in
accordance with paragraph (a) of this section may be relied upon by the
licensee only for use in a single transaction, and for a period not to
exceed 30 calendar days from the date that NICS was initially contacted.
If the transaction is not completed within the 30-day period, the
licensee shall initiate a new NICS check prior to completion of the
transfer.