I just wanted to add a couple of pieces of new information I've recently come across, in case it helps.
Firstly, having learned of Amelia SLACK/SMITH'S marriage in 1869, I just had to order the birth certs of Annie and John PALMER who were supposedly her children.
Well it seems they were John and Mary PALMER'S after all!!! So why say in the parish records that they were the children of Amelia SMITH???

When I found that record very early in my research into this family, I didn't know of any siblings for Mary, so having Amelia's name gave me more to go on in finding her family!
Secondly, and more pertinent to George SLACK's occupation, is that he is down as a Hawker/Pedlar on ALL of his children's baptism records, not just those following the 1851 census in which he said he was a coachmaker!
So to recap, he married Amelia CARNARTON in Jan 1842 and put down coachmaker as his, and his father's, occupation. He also signed his name, which I think is very significant. How many hawkers could write, do you think!
Their first child Ann was born later that year but wasn't christened until 6 Sep 1844, by which time George was a Hawker.
Three more children were christened before the 1851 census at which George was recorded as being a Pedlar.
Then came the 1851 census, and George was suddenly a coachmaker again?!
The baptism of the next child in 1852 sees him, once again, as a Hawker, and so it continues!
Another loose end which has been bugging me throughout, is where George was in 1841.
If he was outside of Cornwall then it could be impossible to find him, but I did come across an entry for a George (surname unknown) born about 1801, living as one of 5 apparently single men, in a house with a variety of people, in St Austell!
Better still, he was a HAWKER!!!!

The only downside was that he was also supposedly born in Ireland!

Anyway, I just thought I'd throw that out in case anyone is interested!