Green’s Dictionary of Slang

tickman n.

also tick-merchant
[one gets the goods ‘on tick’]

(Ulster) a doorstep salesman.

[Ire]P. Boyle At Night All Cats Are Grey 61: The worthy proprietor of this establishment, Mr. Jonty Donoghue [...] whom God preserve from the onslaughts of tinkers, policemen and tick-merchants.
[Ire]J. Morrow Confessions of Proinsias O’Toole 99: It’s an ill wind, Francie: a far cry from the peaceful days when tickmen were wearing out my doorstep.