1874 Glasgow Registry of Parliamentary Voters
Paterson BAMBER, 3 Corunna St, Customs Surveyor, tenant and occupant. (Same address as on the 1868 marriage certificate)
1871, same details except occupation: Customs Officer
1869-70, same, Custom Officer
1868 Paterson BAMBER married,
1871 Paterson BAMBER was a shipping clerk, on the English Census with Georgina, his wife, at West Derby...
(So seems perhaps TWO Paterson BAMBER chaps .... one in Scotland, and one in England ... Father and Son
)Re Mercantile Clerk v Customs Clerk 
Mercantile Clerk for occupation of Georgina's Dad when she married in 1868 in Scotland .... v Customs Clerk for Gordon BLAIR in Ipswich, Queensland in 1865.... As Georgina's Paterson BAMBER's (her father in law) occupation was Customs Surveyor, perhaps "Mercantile Clerk" was a convenient way for Georgina at 16 years of age to describe her Dad.
A Queensland Customs Clerk in the 1860s was a colonial government appointment, and Gordon's express responsibilities would have included charge of the locked powder magazine ... surely any gunpowder storeroom was kept under close supervision, any gunpowder issued would have needed to be well documented, weighed out precisely, careful handling, packaging etc, a 'hands-on' position. Customs at Ipswich would have been involved in assessing any DUTY for imports from other colonies, particularly New South Wales and New Zealand, and of course EXCISE on alcohol etc.
A Mercantile Clerk (in 1860s Qld) would likely be a commercial appointment in the private sector, not a government position.
Re the 1868 marriage The image shows no mention of if Georgina's dad and/or mum was/were already known to be deceased ....

Was it a compulsory question asked by the clergy at that time?
Remember that earlier in this thread there's the 1861 Scottish census showing Jane NORVAL with Georgina and Jane was recorded as a widow
Re Joining dotsI am still having trouble joining dots for Gordon BLAIR in Qld being the husband of Jane NORVAL in Scotland, but regardless, I cannot see that Georgina sought out the Blair family in Qld, or that James William BLAIR sought out Georgina's family when he went to England, as I have not yet found any likely newspaper cuttings re "Missing Friends" or "Missing Relatives" .... or similar.
Re 1901And, answering Rosinish's question, I think in 1901, Paterson Bamber, husband of Georgina was recorded as a Dock Freight Clerk.
Re Asking for further helpExcellent suggestion re asking for specific help. May I suggest similar request on the Australia Board may find RChatter willing to go to Qld State Archives to look up Gordon BLAIR's land file of 1864 and even look up the Probate Files for Gordon and Julia.
JM
ADD : I was posting this around same time as the 're-boot' was kicking in, and some of my sentences got 'mish-mashed' during my copy/paste from a word document, but I have subsequently edited. 11:40am NSW time 24 April 2017.