Listeria is an important-foodborne bacteria. Many people prefer consuming milk products from small-scale retailers. These milk products are not of controlled quality and can cause listeriosis. We explored the possibility of Listeria spp. contamination in milk products from the farm and retailer level. The efficiency of vendors’ processing measures in eliminating L. monocytogenes was also evaluated. Milk samples in the current study were collected from bulk tanks and small-scale milk retailers. As part of the clinical trial, L. monocytogenes-added samples were tested for remaining bacteria after treatment with processing measures employed by the vendors. Descriptive analysis, Chi-squared test, and Fisher’s exact test were used for data analysis. The milk from the farm level presented 1% listeria contamination, which was confirmed to be L. marthii. Data analyses revealed that the location of the retailer was associated with the volume they routinely ordered per lot and the milk-processing time the vendors used to treat milk (p < 0.05). Knowledge on raw milk contamination is significantly associated with the stocking or processing of the whole milk lot. Male sellers reportedly treating milk less thoroughly than their female counterparts (p < 0.01). In clinical trial, L. monocytogenes was not identified after sample treatment.