D. Zhelyzkova, D. Grozeva, and M. Stoyanov, “Risks and Effects of the Activities of Organizations Providing Courier Services and Non-Store Retail Trade in Bulgaria”, НТ, no. 2, pp. 125–157, Aug. 2020, Accessed: Jul. 22, 2026. Available: https://yb.e-dnrs.org/index.php/rp/article/view/5382