Posserman?

[stanmapstone]

And finally, from flourmilling.co.uk:

Posser   A bumping device to assist filling of sacks.

That seems to be the answer for what  a Posserman does  It is surprising that the Oxford English Dictionary does not have that definition.

Stan

[stanmapstone]

Can't say if it's the same one as the one I saw in Census since you've not included any details of the person / place it refers to.

Is it this one?
Stan

I should have said his name is John Goode

Stan

[stanmapstone]

Posser. — An ordinary flour packer by which the flour is not forcibly packed. http://www.rootschat.com/links/01gce/
 I think he should be more properly called a Flour Packer "......packs flour more closely into sack with a punch, or a bumping machine, operated by a foot lever...." part of the job description for a Flour Packer from "A Dictionary of Occupational Terms"
Stan