Like several other artists in Rome, Jenkins judged that he could make a better living as a guide and dealer than as a painter; and in the course of time he became the leading connoisseur and antiquary to British visitors.
[5] In 1770 a dispensation from Pope Clement XIV enabled Jenkins and the painter-dealer Gavin Hamilton to manage the dispersal of the Mattei antiquities, which had formed one of the most-visited private collections in Rome.
Clement made a first selection for his Museo Pio-Clementino at the Vatican before permitting export, with Jenkins and Hamilton acting as agents for Don Giuseppe Mattei.
Essential to Jenkins' modus vivendi was that he was known to everyone, owners of saleable antiquities, Roman and foreign artists and sculptors, and antiquaries like Cardinal Alessandro Albani and Johann Joachim Winckelmann.
[10] By 1792 Jenkins had purchased the manor of Sidmouth near his birthplace; the town was becoming a minor vacation spot, and he built Fortfield Terrace, designed by London architect Michael Novosielski, for visitors.