I have searched FreeBMD from 1851 onwards on the name Samuel Vin* (any spelling after Vin) and can't see a possible marriage.
FreeBMD is not a complete index (but for this period it is very close) of the GRO index. The coverage charts are here, so you can see any quarters that might be worth checking on the GRO index itself.
http://freebmd.rootsweb.com/progressM.shtmlThe GRO index can be viewed quarter by quarter here.
http://www.ancestry.co.uk/search/rectype/vital/freebmd/bmd.aspxThe GRO indexes themselves can be incomplete with errors and mistakes.
The local registrar's office covering the Shepton Mallet area is
Location Mendip
Address
19B Commercial Road
Shepton Mallet
Somerset
Ba4 5BU
Tel +44 (0)1749 343928
Email: SheptonRO
[at]somerset.gov.uk
Registration and Census District (1852 - 1946) 5c
or since by tradition marriages usuallytook place in the bride's parish you could request a search of East Pennard parish registers which are held at Somerset Record Office.
http://www.somerset.gov.uk/archives/Once you have exhausted the local sources if a marriage has still not be found then I think you would have to accept one didn't take place. The church always tried hard to promote official church weddings but it was not until 1754 that the law supported them and jumping back and forth over broomsticks and the like, was still a traditional method which went back many centuries and had the benefit of lacking the costs the church charged for the banns and ceremony itself.
"Informal or common law marriages were legally recognized in England and Wales until they were outlawed in 1754 by Lord Hardwicke’s Act."This article gives the figure in more rural areas in the C19th of up to 1 in 7 marriages 'living tally' i.e.couples who lived together but did not go through a legal ceremony but considered themselves married.
http://www.opo.org.uk/marriedornot/PDF/CommonLawMarriage.pdfRegards
Valda