Grimwade only gives him as entering a bucklemaker mark at 46, Leadenhall Street and does not mention that he was notorious at the time as "Dirty Dick" .
Heal describes him as Hardwareman & Jeweller , No 46 Leadenhall Street.
His Dictionary of National Biography (DNB) entry is summarised below
A celebrated eccentric, the son of a successful City of London merchant. On his father's death in 1760 Bentley inherited ‘a good fortune’ which he used to embellish his existing reputation as ‘the beau of Leadenhall-Street’ well known for his fine manners and dress. In 1764 he visited Paris where he participated in high society, met Louis XVI, and was identified as the best dressed and mannered English gentleman. On his return to London, Bentley maintained his reputation for refinement when in public, and remained a patron of Vauxhall and Ranelagh Gardens until the early nineteenth century.
However, Bentley's celebrity rested less on his fine dress than on the squalor in which he was said to live at his business premises, the so-called ‘dirty warehouse’ at 46 Leadenhall Street. Several pamphlets published at the turn of the century claimed that the shop had not been cleaned since his father's death, and speculated on the existence of a dining room that had been shut up following the death of Bentley's fiancée shortly before their intended marriage. Bentley's appearance and mannerisms also attracted considerable attention. Unwashed and dressed in shirt sleeves and an ill-powdered wig, he refused offers for his house to be cleaned claiming that its notoriety was good for trade. Certainly his reputation attracted a number of female visitors intrigued by rumours of his miserliness, the infamous ‘blue room’, and his supposed habit of sleeping in a coffin. In fact the majority emerged to speak of the gentlemanliness beneath the grime, politeness being ‘his ruling passion’.
Thou art ('tis said) a very comely man,
Of polish'd language, partial to the fair,
Then why not wash thy face, and comb thy matted hair?
(European Magazine, January 1801)
In February 1804 Bentley left 46 Leadenhall Street when the lease expired.. Thereafter Bentley lived in Jewry Street, Aldgate, until 1807 and then at Leonard Street, Shoreditch, for a further year before he took up as a beggar and travelled the country. After a brief period at Musselburgh, Midlothian, he moved to nearby Haddington where he died, unmarried, from fever in 1809.
I have never seen any buckles bearing his mark