"Personally I find the Blind Beggar plot not merely implausible as a true story but not even very convincing fiction"
Pepys connected the broadside to an Eating House he frequented run by such a character in East London and describes a visit to it in his diary
"This very house was built by the blind beggar of Bethnal Grren so much talked of and sang in the ballads"   
Bishop Percy in his Reliques connects the character to a soldier who was blinded in The Battle of Evesham in 1265
Somewhat coincidentally, we recorded this first on a Travellers site just off the Mile End Road in East London, a few minutes walk from the 'Blind Beggar' pub, which was the hang-out of notorious gangsters, The Kray Brothers.
Of course the 'rich beggar' character in folklore owes much to the legend of James V (1512-1542), the hanger of Johnny Armstrong, who reputably wandered his kingdom in disguise, often as a beggar, as 'The Guidman of Ballangeich'
"The ballad writers in all centuries took their inspiration from a wide range of sources, folk tales, higher literature, newspapers"
As far as the broadside writers are concerned, there is no evidence whatever of where they took their inspiration from - we have no idea who they were, with very few exceptions
Working as they did, they appear to have written almost automatically to a set formula in order to produce as many songs as possible in the shortest time.
This is where the two-way process you raised in your talk possible came in
Lile today's pop industry, the trade wa a predatory one where the song sellers would get their goods wherever they could
If country singers, sailors, soldiers..... were in town and accessible, they surely would have been regarded as a rich source of material to be printed and sold
You only have to look at the collections I mentioned to see that there appeared to be very little artistic creation in their making, none of the subtleties that you find in folk song and certainly none of the humanity
In folk song ou get sentiment and compassion, in the broadsides you get (often very exaggerated) snitmentality
Jim Carroll