Hi Jan
The 1879 death you have found on GR is probably the Chelmondiston one as per my earlier post.
As for the marriages you are quoting the 1825 marriage is probably also relates to Chelmondiston. John SCARF to Mary Brown 17 Apr 1825 Chelmondiston. The 1820 one could be John SCARFE to Sarah ELLIS 5 Feb 1820 Old Newton (Suffolk marriage Index). There are quite a few John Scarf marriages listed between 1813-37 just none to a Mary Ann that would fit your chap but as she was from Essex it is quite feasible that they married there. The only way to clarify the situation is to get a copy of the birth cert for William from the GRO.
Put little store on family trees you see on line many are wildly wrong. People seem to forget there was no such thing as computers in the 1800s & now not all the records have been transcribed and are available online certainly not in Suffolk. Part of your problem seems to be that the LDS (familysearch.org) has not been able to transcribe the East Bergholt PRs thats why you are struggling to find the info you need online.
Try & find John SCARFE c1805 on the 1851CR - what was his marital status. If he had a wife who?
The Suffolk Family History Society does sell CDs for baptisms in the Samford area 1754-1900 it includes East bergholt. Check out their website for info
http://www.suffolkfhs.co.uk/osc/index.php?cPath=31_35K