Your best-intentioned customer-facing employees can still create a poor impression with customers from a different part of the world due to cultural differences of which they’re not aware. (The same may be true when they interact with a different subculture within their same country as well.)
Culture is the set of assumptions, traditions, and values a community develops over time. Thus, members of a culture other than yours may interpret your behavior in ways that haven’t occurred to you, because of their community’s own assumptions, traditions, or values.