He was a hosier up until about 1790 and living at 99 Minories London. He married an Ann Pinchback in 1785. I then have him as the grocer and tea merchant after 1793 at Burr St. I am guessing he was born around 1754 but there does not seem to be any blacksmith reference. I have seen a reference to one of his sons Nathaniel Davis being a freeman blacksmith in 1817 but he was a wine merchant at the time.
An odd mix of occupations.
A blacksmith would have required an apprenticeship, probably 7 years. Some apprenticeship records exist from 18th-early 19thC . Apprenticeship agreements were drawn up between the master and parent or guardian of apprentice. There was a tax on these. Some boys learned the craft from father or other relative with no formal agreement so no record.
John and Nathaniel Davis may not have worked as blacksmiths or if they did, only for a short time. They may have been members of the Worshipful Company of Blacksmiths. It was one of the Livery Companies of the City of London. Another Livery Company was the Grocers' Company; I wonder why they didn't join that. Livery Companies were set up in medieval era. Trading within city boundaries was restricted to members of Livery Companies. Blacksmiths had moved outside the City of London by late 18th century and the Worshipful Company gave up its' hall in 1785. Liverymen are entitled to vote for the Lord Mayor.
Worshipful Company of Blacksmiths website
https://blacksmithscompany.co.uk In particular, read sections 'History' and 'City links'. Mentions 'free blacksmith'.
I thought the connection may have been Smithfield but that was the old site of the cattle and meat markets. Then I had a lightbulb moment about guilds.