I feel like I need a score card; several very valid points have been made on both sides of this question!
First a foremost, I don't think it's truly fair to tell Shoptastic that they're over-thinking or being too much of a perfectionist. Each of us have our own ways of doing things, have our own sets of circumstances under which we've been raised and experienced life in general. We have very individual perceptions of the situations around us and--even when objectively recording and reports facts--have experienced those "facts" quite differently than someone who might have been standing beside us and experiencing the exact same thing at the exact same time. It's part of the human condition, really, and it is why police can have three eye-witnesses to a single crime that yield three completely different versions of what happened. It is also precisely the reason that any good MSP when designing the methodology for the evaluations that we do will have multiple shoppers evaluating the same employees during various situations--because that single employee might very well have been in the exact same mood during three separate evaluations that were simply perceived in three different ways. It is true, I will add, that it becomes the job of the analysts and the clients themselves to qualitatively quantify the results in relations to individual employees.
I applaud Shoptasitc's attention to detail and demonstration of an attitude that says she truly cares about the quality of the work submitted and isn't motivated by simply bottom line profit margins and completing more evaluations in a given time to increase them.
As far as the question itself, regarding cultural differences the the influence they have on things such as friendliness, I think the answer is a resounding, "Yes, they absolutely play a role!" It is our mission as objective observers to report the facts as facts and when asked for our opinions or feelings (i.e., interpretations of those facts) it is imperative to remember that often (realistically, more often than not) the cultural influence at play is really our own uniquely American attitude of entitlement and what it means for an employee to exhibit friendliness and "warmth." Prettygul1 added an invaluable insight, in my opinion, in that he/she brought into the equation the different levels of "friendliness" and questions of how APPROPRIATE they might be contextually.
For me to rate (on a scale of 1 to 10) an employee with whom I;ve just had an retail interaction as a 10 on the "Friendly Scale" isn't the same as someone I might have met a cocktail party. That same person who got a 10 in the retail world, might only get a 5 in a social setting. Whereas a person getting a 10 in that social setting, who displayed the same level of "friendliness" the next day as I was buying boxer shorts, might likely have been rated as N/A - Employee clearly a stalker with psychotic tendencies.
Good on you, SHoptastic, for caring about the work you're doing and the potential effect it might have on those you are evaluating. Err on the side of caution is my own best advice to myself in similar situations, and wherever I can, I make use of the "Extra thoughts" questions most reports have near the end. There I can make any caveats to things rated earlier, add context or interpretation.