I think John Purkis had a sister called Ann who married John Squibb in 1779.
When John Purkis married Sarah King he gave his surname as Purkies.
https://search.findmypast.co.uk/reco...hlights=%22%22
When his sister Ann married John Squibb he was a witness, with Phebe? Purkies.
https://search.findmypast.co.uk/reco...hlights=%22%22
The signatures for John Purkies look the same. Note the curl on the J of John.
So now I have to look for the parents of Ann, John and possibly Phebe Purki(e)s.